Interpretation of Diagnostic Tests
8th Edition

12
Metabolic and Hereditary Disorders
Acid-Base Disorders
pH represents the negative logarithm of H+ concentration; changes nonlinearly masking magnitude of acid-base disorders.
In analyzing acid-base disorders, several points should be kept in mind:
  • Determination of pH and blood gases should preferentially be performed on arterial blood. Venous blood is useless for judging oxygenation or if perfusion is not adequate, but it offers an estimate of acid-base status. Venous pH is ∼0.03 to 0.04 lower than in arterial blood, and CO2 pressure (pCO2)is normally ∼3 to 4 mm higher.
  • Blood specimens should be packed in ice immediately; a delay of even a few minutes will cause erroneous results, especially if the white blood cell (WBC) count is high.
  • Determination of electrolytes, pH, and blood gases should be performed on blood specimens obtained simultaneously, since the acid-base situation may be very labile.
  • Repeated determinations are often indicated because of the development of complications, the effect of therapy, and other factors.
  • Acid-base disorders are often mixed rather than in the pure form. These mixed disorders may represent simultaneously occurring diseases, complications superimposed on the primary condition, or the effect of treatment.
  • Changes in chronic forms may be notably different from those in the acute forms.
  • For judging hypoxemia, it is also necessary to know the patient’s hemoglobin (Hb) or hematocrit (Hct) and whether the patient was breathing room air or oxygen when the specimen was drawn.
  • Arterial blood gases cannot be interpreted without clinical information about the patient.
Renal compensation for a respiratory disturbance is slower (3 to 7 days) but more successful than respiratory compensation for a metabolic disturbance but cannot completely compensate for arterial CO2 pressure (PaCO2) >65 mm Hg, unless another stimulus for HCO3 retention is present. The respiratory mechanism responds quickly but can only eliminate sufficient CO2 to balance the most mild metabolic acidosis.
Most laboratories measure pH and pCO2directly and calculate HCO3 using the Henderson-Hasselbalch equation:
Arterial pH = 6.1 + log [(HCO3) + (0.03 × pCO2)]
where 6.1 is the dissociation constant for CO2 in aqueous solution and 0.03 is a constant for the solubility of CO2 in plasma at 37°C.
Table 12-1. Metabolic and Respiratory Acid-Base Changes in Blood
  pH pCO2 HCO3-
Acidosis
  Acute metabolic D N D
  Compensated metabolic N D D
  Acute respiratory D I N
  Compensated respiratory N I I
Alkalosis
  Acute metabolic I N I
  Chronic metabolic I I I
  Acute respiratory I D N
  Compensated respiratory N D D
D = decreased; I = increased; N = normal.
Table 12-2. Illustrative Serum Electrolyte Values in Various Conditions
Condition pH HCO3- Potassium Sodium Chloride
Normal 7.35–7.45 24–26 3.5–5.0 136–145 100–106
Metabolic acidosis
  Diabetic acidosis 7.2 10 5.6 122 80
  Fasting 7.2 16 5.2 142 100
  Severe diarrhea 7.2 12 3.2 128 96
  Hyperchloremic acidosis 7.2 12 5.2 142 116
  Addison’s disease 7.2 22 6.5 111 72
  Nephritis 7.2 8 4.0 129 90
  Nephrosis 7.2 20 5.5 138 113
Metabolic alkalosis
  Vomiting 7.6 38 3.2 150 94
  Pyloric obstruction 7.6 58 3.2 132 42
  Duodenal obstruction 7.6 42 3.2 138 49
Respiratory acidosis 7.1 30 5.5 142 80
Respiratory alkalosis 7.6 14 5.5 136 112
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A normal pH does not ensure the absence of an acid-base disturbance if the pCO2 is not known.
An abnormal HCO3 indicates a metabolic rather than a respiratory problem;
  • Decreased HCO3-indicates metabolic acidosis.
  • Increased HCO3- indicates metabolic alkalosis.
  • Respiratory acidosis is associated with a pCO2 >45 mm Hg.
  • Respiratory alkalosis is associated with a pCO2 <35 mm Hg.
  • Thus, mixed metabolic and respiratory acidosis is characterized by low pH, low HCO3-, and high pCO2.
  • Mixed metabolic and respiratory alkalosis is characterized by high pH, high HCO3-, and low pCO2.
In severe metabolic acidosis, respiratory compensation is limited by inability to hyperventilate pCO2 to<∼15 mmHg; beyond that, small increments of the H+ ion produce disastrous changes in pH and prognosis; thus patients with lung disorders (e.g., chronic obstructive pulmonary disease [COPD], neuromuscular weakness) are very
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vulnerable because they cannot compensate by hyperventilation. In metabolic alkalosis, respiratory compensation is limited by CO2 retention, which rarely causes pCO2
>50 to 60 mm Hg (because increased CO2 and hypoxemia stimulate respiration very strongly); thus, pH is not returned to normal.
Table 12-3. Upper Limits of Arterial Blood pH and HCO3- Concentrations (Expected for Blood pCO2 Values)
Arterial Blood HCO3- (mEq/ L)
pCO2 (mm Hg) pH
20 7.66 22.8
30 7.53 25.6
40 7.57 27.3
60 7.29 27.9
80 7.18 28.9
Values shown are the upper limits of the 95% confidence bands.
Source: Coe FL. Metabolic alkalosis. JAMA 1977;238:2288.
Table 12-4. Summary of Pure and Mixed Acid-Base Disorders
  Decreased pH Normal pH Increased pH
Increased pCO2 Respiratory acidosis with or without incompletely compensated metabolic alkalosis or coexisting metabolic acidosis Respiratory acidosis and compensated metabolic alkalosis Metabolic alkalosis with incompletely compensated respiratory acidosis or coexisting respiratory acidosis
Normal pCO2 Metabolic acidosis Normal Metabolic alkalosis
Decreased pCO2 Metabolic acidosis with incompletely compensated respiratory alkalosis or coexisting respiratory alkalosis Respiratory alkalosis and compensated metabolic acidosis Respiratory alkalosis with or without incompletely compensated metabolic acidosis or coexisting metabolic alkalosis
Source: Adapted from Friedman HH. Problem-oriented medical diagnosis, 3rd ed. Boston: Little, Brown, 1983.
Base excess (BE) is a number that hypothetically “corrects” pH to 7.40 by first “adjusting” pCO2 to 40 mmHg, thereby allowing comparison of resultant HCO3- with normal value at that pH (24 mEq/L). Normal = –2 to +2 mEq/L.
BE can be calculated from by determined values for pH and HCO3- by this formula:
BE (mEq/L) = HCO3- + 10(7.40 - pH) - 24
Negative BE indicates depletion of HCO3-. It does not distinguish primary from compensatory derangement.
(1) Respiratory Alkalosis
Respiratory alkalosis is defined as a decreased pCO2 of <38 mm Hg.
Caused By
Hyperventilation
  • Central nervous system (CNS) disorders (e.g., infection, tumor, trauma, cerebrovascular accident, anxiety-hyperventilation)
  • Hypoxia (e.g., high altitudes, ventilation-perfusion imbalance)
    • Cardiovascular (e.g. congestive heart failure, hypotension)
    • Pulmonary disease (e.g., pneumonia, pulmonary emboli, asthma, pneumothorax)
  • Drugs (e.g., salicylate intoxication, methylxanthines, β-adrenergic agonists)
  • Metabolic (e.g., acidosis [diabetic, renal, lactic], liver failure)
  • Others (e.g., fever, pregnancy, Gram-negative sepsis, pain)
  • Mechanical overventilation, cardiopulmonary bypass
Laboratory Findings
Acute hypocapnia—usually only a modest decrease in plasma HCO3- concentrations and marked alkalosis
Chronic hypocapnia—usually only a slight alkaline pH (not usually >7.55)
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Fig. 12-1. Algorithm for acid-base imbalance and anion gap (AG).
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Fig. 12-2. Algorithm illustrating effects of metabolic and respiratory acid-base changes in blood.
(2) Respiratory Acidosis
Laboratory findings differ in acute and chronic conditions.
(2a) Acute
Caused by decreased alveolar ventilation impairing CO2 excretion:
  • Cardiopulmonary (e.g., pneumonia, pneumothorax, pulmonary edema, foreign body aspiration, laryngospasm, bronchospasm, mechanical ventilation, cardiac arrest)
  • CNS depression (e.g., general anesthesia, drugs, brain injury, infection)
  • Neuromuscular (e.g., Guillain-Barré syndrome, hypokalemia, myasthenic crisis)
Acidosis is severe (pH 7.05–7.10), but HCO3- concentration is only 29 to 30 mEq/L.
Severe mixed acidosis is common in cardiac arrest, when respiratory and circulatory failure causes marked respiratory acidosis and severe lactic acidosis.
Table 12-5. Immediate and Delayed Compensatory Response to Acid-Base Disturbances
Acid-Base Abnormality Immediate Response (By Lungs) Delayed Response (By Kidneys)
Respiratory alkalosis (1) ↑pCO2 by decreasing ventilation ↓HCO3- excretion.
↓Acid excretion
Respiratory acidosis (2) ↓pCO2 by increasing ventilation ↑HCO3- retention.
↑Acid excretion
Metabolic alkalosis (3) ↑pCO2 by decreasing ventilation ↓HCO3- excretion.
↓Acid excretion
Metabolic acidosis (4) ↓pCO2 by increasing ventilation ↑HCO3- retention.
↑Acid excretion
↑, increases;  ↓, decreases.
Table 12-6. Primary Change, and Compensatory Mechanisms in Delayed Response to, and Chloride Level in Acid-Base Disturbances
  Primary Change Compensatory Mechanism Delayed Response (By Kidneys) Cl-
Respiratory alkalosis (1) ↓pCO2 None. ↓HCO3 3–5 mmol/L for every 10 mm Hg ↑pCO2
Respiratory acidosis (2) ↑pCO2 ↑HCO3- 1 mmol/L for every 10 mm Hg↑pCO2. ↑HCO3- 3–5 mmol/L for every 10 mm Hg ↑pCO2.
Metabolic alkalosis (3) ↑HCO3- ↑pCO2 3–5 mm Hg for every 10 mmol/L ↑HCO3- ↓HCO3- excretion.
↓Acid excretion
Metabolic acidosis with increased anion gap (4a) ↓HCO3- ↓pCO2 1.0–1.3 mm Hg mmol/L for every 1 mmol/L ↑HCO3- ↑HCO3- retention
↑Acid excretion
No change
Metabolic acidosis normal anion gap (4b) ↓HCO3- pCO2 changes 2 for every pH change after decimal (e.g., if pH = 7.25, pCO2 = 25 ± 2).  
Respiratory alkalosis (1) ↓pCO2 Acute: none
Chronic: ↓HCO3- 3–5 mmol/L for every 10 mm Hg ↑pCO2.
 
Respiratory acidosis (2) ↑pCO2 Acute: ↑HCO3- 1 mmol/L for every 10 mm Hg ↑pCO2
Chronic: ↑HCO3- 3–5 mmol/L for every 10 mm Hg ↑pCO2
 
Metabolic alkalosis (3) ↑HCO3- ↑pCO2 3 to 5 mm Hg for every 10 mmol/L ↑HCO3-  
Metabolic acidosis with increased anion gap (4a) ↓HCO3- ↓pCO2 1.0–1.3 mm Hg for every 1 mmol/L ↓HCO3-   No change
Metabolic acidosis with normal anion gap (4b) ↓HCO3- pCO2 changes 2 for every pH change after decimal (e.g., if pH = 7.25, pCO2 = 25±2) Hyperchloremic metabolic acidosis  
↑, increased;  ↓, decreased.
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(2b) Chronic
Due to chronic obstructive or restrictive conditions
  • Nerve disease (e.g., poliomyelitis)
  • Muscle disease (e.g., myopathy)
  • CNS disorder (e.g., brain tumor)
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  • Restriction of thorax (e.g., musculoskeletal, scleroderma, Pickwickian syndrome)
  • Pulmonary disease (e.g., prolonged pneumonia, primary alveolar hypoventilation)
Acidosis is not usually severe.
Beware of commonly occurring mixed acid-base disturbances (e.g., chronic respiratory acidosis with superimposed acute hypercapnia resulting from acute infection, such as bronchitis or pneumonia).
Superimposed metabolic alkalosis (e.g., due to diuretics or vomiting) may exacerbate the hypercapnia.
(3) Metabolic Alkalosis
Caused By
Loss of acid:
  • Vomiting, gastric suction, gastrocolic fistula
  • Diarrhea in mucoviscidosis (rarely)
  • Villous adenoma of colon
  • Aciduria secondary to potassium depletion
Excess of base caused by administration of:
  • Absorbable antacids (e.g., sodium bicarbonate; milk-alkali syndrome)
  • Salts of weak acids (e.g., sodium lactate, sodium or potassium citrate)
  • Some vegetarian diets
  • Citrate due to massive blood transfusions
Potassium depletion (causing sodium and H+ to enter the cells):
  • Gastrointestinal (GI) loss (e.g., chronic diarrhea)
  • Lack of potassium intake (e.g., anorexia nervosa, intravenous fluids without potassium supplements for treatment of vomiting or postoperatively)
  • Diuresis (e.g., mercurials, thiazides, osmotic diuresis)
  • Extracellular volume depletion and chloride depletion
  • Dehydration reducing intracellular volume, thereby stimulating aldosterone, causing excretion of potassium and H+
  • All forms of mineralocorticoid excess (e.g., primary aldosteronism, Cushing syndrome, administration of steroids, large amounts of licorice) causing excretion of potassium and H+
  • Glycogen deposition
  • Chronic alkalosis
  • Potassium-losing nephropathy
Hypoproteinemia per se may cause a nonrespiratory alkalosis. Decreased albumin of 1g/dL causes an average increase in standard bicarbonate of 3.4 mmol/L, an apparent base excess of +3.7 mEq/L, and a decrease in anion gap (AG) of ∼3 mEq/L.
Laboratory Findings
Serum pH is increased (>7.60 in severe alkalemia).
Total plasma CO2 is increased (bicarbonate >30 mEq/L).
pCO2 is normal or slightly increased.
Serum pH and bicarbonate above those predicted by the pCO2 (by nomogram or Table 12-3).
Hypokalemia is an almost constant feature and is the chief danger in metabolic alkalosis.
Decreased serum chloride is relatively lower than sodium.
Blood urea nitrogen (BUN) may be increased.
Urine pH is >7.0 (≤7.9) if potassium depletion is not severe and concomitant sodium deficiency (e.g., vomiting) is not present. With severe hypokalemia (<2.0 mEq/L), urine may be acid in presence of systemic alkalosis.
  • Metabolic alkalosis patients may be volume depleted and chloride responsive or have volume expansion and be chloride resistant. When the urine chloride is low (<10 mEq/L) and the patient responds to chloride treatment, the cause is more likely loss of gastric juice, diuretic therapy, or rapid relief of chronic hypercapnia. Chloride replacement is completed when urine chloride remains >40 mEq/L. When the urine chloride is high (>20 mEq/L) and the patient does not respond to NaCl treatment, the cause is more likely hyperadrenalism or severe potassium deficiency.
Fig. 12-3. Acid-base map. The values demarcated for each disorder represent a 95% probability range for each pure disorder. Coordinates lying outside these zones suggest mixed acid-base disorders. N, normal. (Adapted from
Goldberg M, Green SB, Moss ML, et al. Computer-based instruction and diagnosis of acid-base disorders. JAMA 1973;223:269.
)
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Acid-base maps (see Figure 12-3) are a graphic solution of the Henderson-Hasselbalch equation, which predicts the HCO3- value for each set of pH/pCO2 coordinates. They also allow a check of the consistency of arterial blood gas and automated analyzer determinations, since these may determine the total CO2 content, of which 95% is HCO3-. These maps contain bands that show the 95% probability range of values for each disorder. If the pH/pCO2 coordinate is outside the 95% confidence band, then the patient has at least two acid-base disturbances. These maps are of particular use when one of the acid-base disturbances is not suspected clinically. If the coordinates lie within a band, it is not a guarantee of a simple acid-base disturbance.
Anion Gap Classification
AG is arithmetic approximation of difference between routinely measured serum anions and cations = 23 mEq/L minus 11 mEq/L = 12 mEq/L.
Unmeasured ions include proteins (mostly albumin) = 15 mEq/L, organic acids = 5 mEq/L, phosphates = 2 mEq/L, sulfates = 1 mEq/L; total = 23 mEq/L.
Unmeasured cations include calcium = 5 mEq/L, potassium = 4.5 mEq/L, magnesium = 1.5 mEq/L; total = 11 mEq/L.
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Calculated as Na+ – (Cl- + HCO3-); typical normal values = 8 to 16 mEq/L; if K+ is included, normal=10 to 20 mEq/L; reference interval varies considerably depending on instrumentation and between individuals. Increased AG reflects amount of organic (e.g., lactic acid, ketoacids) and fixed acids present.
AG initially began as a measure of quality assurance.
Use
Identify cause of a metabolic acidosis
Supplement to laboratory quality control, along with its components
Increased AG In
  • Increased “unmeasured” anions
    • Organic (e.g., lactic acidosis, ketoacidosis)
    • Inorganic (e.g., administration of phosphate, sulfate)
    • Protein (e.g., hyperalbuminemia, transient)
    • Exogenous (e.g., salicylate, formate, paraldehyde, nitrate, penicillin, carbenicillin)
    • Not completely identified (e.g., hyperosmolar hyperglycemic nonketotic coma, uremia, poisoning by ethylene glycol, methanol)
    • Artifactual
      Falsely increased serum sodium
      Falsely decreased serum chloride or bicarbonate
  • When AG>12 to 14 mEq/L, diabetic ketoacidosis is the most common cause, uremic acidosis is the second most common cause, and drug ingestion (e.g., salicylates, methyl alcohol, ethylene glycol, ethyl alcohol) is the third most common cause; lactic acidosis should always be considered when these three causes are ruled out. In small children, rule out inborn errors of metabolism.
  • Mnemonic for AG acidosis: A MUDPIE: A, aspirin; M, methyl alcohol; U, uremia; D, diabetic acidosis; P, propyl alcohol or paraldehyde administration; I, isopropyl alcohol or idiopathic lactic acidosis; E, ethylene glycol.
Decreased AG (<6 mEq/L) In
  • Decreased unmeasured anion (e.g., hypoalbuminemia is probably commonest cause of decreased AG); also hypocalcemia, hypomagnesemia.
  • Artifactual
    • “Hyperchloremia” in bromide intoxication (if chloride determination by colorimetric method)
    • False increase in serum chloride or HCO3-
    • False decrease in serum sodium (e.g., hyperlipidemia, hyperviscosity)
  • Increased unmeasured cations
    • Hyperkalemia, hypercalcemia, hypermagnesemia
    • Increased proteins in multiple myeloma, paraproteinemias, polyclonal gammopathies (these abnormal proteins are positively charged and lower the AG)
    • Increased lithium, tris buffer (tromethamine)
  • AG>30 mEq/L almost always indicates organic acidosis, even in presence of uremia.
    AG = 20 to 29 mEq/L occurs in absence of identified organic acidosis in 25% of patients.
    AG is rarely>23 mEq/L in chronic renal failure.
Simultaneous changes in ions may cancel each other out, leaving AG unchanged (e.g., increased Cl and decreased HCO3-).
Change in AG should equal change in HCO3-; otherwise a mixed rather than simple acid-base disturbance is present.
(4) Metabolic Acidosis
(4a) With Increased Anion Gap (AG >15 mEq/L)
Lactic acidosis—commonest cause of metabolic acidosis with increased AG (frequently >25 mEq/L) (see following section)
Renal failure (AG <25 mEq/L)
Ketoacidosis
  • Diabetes mellitus (AG frequently >25 mEq/L)
  • Associated with alcohol abuse (AG frequently 20 to 25 mEq/L)
  • Starvation (AG usually 5 to 10 mEq/L)
Drugs
  • Salicylate poisoning (AG frequently 5 to 10 mEq/L; higher in children)
  • Methanol poisoning (AG frequently >20 mEq/L)
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  • Ethylene glycol poisoning (AG frequently >20 mEq/L)
  • Paraldehyde (AG frequently >20 mEq/L)
(4b) With Normal Anion Gap (AG)
Hyperchloremic metabolic acidosis
Decreased serum potassium
  • Renal tubular acidosis (RTA)
    • Acquired (e.g., drugs, hypercalcemia)
    • Inherited (e.g., cystinosis, Wilson disease)
    • Carbonic anhydrase inhibitors (e.g., acetazolamide, mafenide)
  • Increased loss of alkaline body fluids (e.g., diarrhea, loss of pancreatic or biliary fluids)
  • Ureteral diversion (e.g., ileal bladder or ureter, ureterosigmoidostomy)
Normal or increased serum potassium
  • Hydronephrosis
  • Early renal failure
  • Administration of HCl (e.g., ammonium chloride)
  • Hypoadrenalism (diffuse, zona glomerulosa, or hyporeninemia)
  • Renal aldosterone resistance
  • Sulfur toxicity
In lactic acidosis, the increase in AG is usually greater than the decrease in HCO3-, in contrast to diabetic ketoacidosis, in which the increase in AG is identical to the decrease in HCO3-.
Laboratory Findings
Serum pH is decreased (<7.3).
Total plasma CO2 content is decreased; <15 mEq/L almost certainly rules out respiratory alkalosis.
Serum potassium is frequently increased; it is decreased in RTA, diarrhea, or carbonic anhydrase inhibition. Increased serum chloride.
Azotemia suggests metabolic acidosis due to renal failure.
Urine is strongly acid (pH = 4.5–5.2) if renal function is normal.
In evaluating acid-base disorders, calculate the AG (see previous).
Lactic Acidosis
Indicates acute hypoperfusion and tissue hypoxia.
Should be considered in any metabolic acidosis with increased AG (>15 mEq/L).
Diagnosis is confirmed by exclusion of other causes of metabolic acidosis and serum lactate ≥5 mEq/L (upper limit of normal = 1.6 for plasma and 1.4 for whole blood). There is considerable variation in the literature in limits of serum lactate and pH to define lactic acidosis.
Exclusion of other causes by
  • Normal serum creatinine and BUN (increased acetoacetic acid [but not beta-hydroxybutyric acid] will cause false increase of creatinine by colorimetric assay)
  • Osmolar gap <10 mOsm/L
  • Negative nitroprusside reaction (nitroprusside test for keto-acidosis measures acetoacetic acid but notβ-hydroxybutyric acid; thus blood ketone test may be negative in diabetic ketoacidosis)
  • Urine negative for calcium oxalate crystals
  • No known ingestion of toxic substances
Laboratory findings due to underlying diseases (e.g., diabetes mellitus, renal insufficiency, etc.)
Laboratory tests for monitoring therapy:
  • Arterial pH, pCO2, HCO3-, serum electrolytes every 1 to 2 hours until patient is stable
  • Urine electrolytes every 6 hours
Associated or compensatory metabolic or respiratory disturbances (e.g., hyperventilation or respiratory alkalosis may result in normal pH)
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Caused By
Type A due to tissue hypoxia (e.g., acute hemorrhage, severe anemia, shock, asphyxia), marathon running, seizures
Type B without tissue hypoxia caused by:
  • Common disorders (e.g., diabetes mellitus, uremia, liver disease, infections, malignancies, alkaloses)
  • Drugs and toxins (e.g., ethanol, methanol, ethylene glycol, salicylates, metformin)
  • Hereditary enzyme defects (e.g., methylmalonic acidemia, propionic aciduria, defects of fatty acid oxidation, pyruvate-dehydrogenase deficiency, pyruvate-carboxylase deficiency, multiple carboxylase deficiency, glycogen storage disease [GSD] type I).
  • Others (e.g., starvation, short-bowel syndrome)
With a typical clinical picture (acute onset following nausea and vomiting, altered state of consciousness, hyperventilation, high mortality)
  • Decreased serum bicarbonate
  • Low serum pH, usually 6.98 to 7.25
  • Increased serum potassium, often 6 to 7 mEq/L
  • Serum chloride normal or low with increased AG
  • •Increased serum phosphorus. Phosphorus:creatinine ratio >3 indicates lactic acidosis either alone or as a component of other metabolic acidosis.
  • WBC count is increased (occasionally to leukemoid levels).
  • Increased serum uric acid is frequent (up to 25 mg/dL in lactic acidosis)
  • Increased serum aspartate aminotransferase (AST), lactase dehydrogenase (LD), and phosphorus
(5) Mixed Acid-Base Disturbances
Mixed acid-base disturbances must always be interpreted with clinical data and other laboratory findings.
(5a) Respiratory Acidosis with Metabolic Acidosis
Examples: Acute pulmonary edema, cardiopulmonary arrest (lactic acidosis due to tissue anoxia and CO2 retention due to alveolar hypoventilation)
Acidemia may be extreme with
  • pH <7.0 (H+ >100 mEq/L)
  • HCO3- <26 mEq/L. Failure of HCO3- to increase ≥3 mEq/L for each 10 mm Hg rise in pCO2 suggests metabolic acidosis with respiratory acidosis.
Mild metabolic acidosis superimposed on chronic hypercapnia causing partial suppression of HCO3- may be indistinguishable from adaptation to hypercapnia alone.
(5b) Respiratory Acidosis with Metabolic Alkalosis
Examples: Chronic pulmonary disease with CO2 retention developing metabolic alkalosis due to administration of diuretics, severe vomiting, or sudden improvement in ventilation (“posthypercapnic” metabolic alkalosis)
  • Decreased or absent urine chloride indicates that chloride-responsive metabolic alkalosis is a part of the picture.
  • In clinical setting of respiratory acidosis but with normal blood pH and/or HCO3- higher than predicted, complicating metabolic alkalosis may be present.
(5c) Metabolic Acidosis with Respiratory Alkalosis
Examples: Rapid correction of severe metabolic acidosis, salicylate intoxication, Gram-negative septicemia, initial respiratory alkalosis with subsequent development of metabolic acidosis. Primary metabolic acidosis with primary respiratory alkalosis with an increased AG is characteristic of salicylate intoxication in absence of uremia and diabetic ketoacidosis.
Table 12-7. Illustrative Serum Values in Acid-Base Disturbances
Condition Sodium (mEq/L) Chloride (mEq/L) HCO3- (mEq/L) pCO2 (mm Hg) pH
Normal 140 105 25 40 7.40
Metabolic acidosis 140 115 15 31 7.30
Chronic respiratory alkalosis 136 102 25 40 7.44
Mixed metabolic acidosis and chronic respiratory alkalosis (e. g., sepsis: addition of respiratory alkalosis to metabolic acidosis further decreases HCO3- but pH may remain normal; lactic acidosis plus respiratory alkalosis due to severe liver disease, pulmonary emboli, or sepsis 136 108 14 24 7.39
Metabolic alkalosis 140 92 36 48 7.49
Chronic respiratory acidosis 140 100–102 28 50 7.37
Mixed metabolic alkalosis and chronic respiratory acidosis (e. g., patient with COPD receiving glucocorticoids or diuretics; pCO2 and HCO3- are increased by both conditions, but pH is neutralized) 140 90 40 67 7.40
Metabolic alkalosis 139 89 35 47 7.49
Respiratory alkalosis 136 102 20 30 7.44
Mixed alkalosis, mild 139 92 32 39 7.53
Mixed alkalosis, severe (e.g., postoperative patient with severe hemorrhage stimulating hyperventilation [respiratory alkalosis] plus massive transfusion and nasogastric drainage [metabolic alkalosis]) 139 92 32 30 7.63
Mixed chronic respiratory acidosis and acute metabolic acidosis (e.g., COPD [chronic respiratory acidosis] with severe diarrhea [metabolic acidosis]. pH is too low for pCO2 of 55 mm Hg in chronic respiratory acidosis, indicating low pH due to mixed acidosis, but HCO3- effect is offset.) 136 102 22 55 7.22
Mixed metabolic acidosis and metabolic alkalosis (e.g., gastroenteritis with vomiting [metabolic alkalosis] and diarrhea [metabolic acidosis due to loss of HCO3-]; surprisingly normal findings with marked volume depletion) 140 103 25 40 7.40
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pH may be normal or decreased.
Hypocapnia remains inappropriate to decreased HCO3- for several hours or more.
(5d) Metabolic Alkalosis with Respiratory Alkalosis
Examples: Hepatic insufficiency with hyperventilation plus administration of diuretics or severe vomiting; metabolic alkalosis with stimulation of ventilation (e.g., sepsis, pulmonary embolism, mechanical ventilation), which causes respiratory alkalosis
Marked alkalemia with decreased pCO2 and increased HCO3- is diagnostic.
(5e) Acute and Chronic Respiratory Acidosis
Examples: Chronic hypercapnia with acute deterioration of pulmonary function causing further rise of pCO2.
May be suspected when HCO3- is in intermediate range between acute and chronic respiratory acidosis (similar findings in chronic respiratory acidosis with superimposed metabolic acidosis or acute respiratory acidosis with superimposed metabolic alkalosis)
(5f) Coexistence of Metabolic Acidosis of Hyperchloremic Type and Increased AG
Examples: uremia and proximal RTA, lactic acidosis with diarrhea, excessive administration of NaCl to patient with organic acidosis
May be suspected by plasma HCO3- that is lower than is explained by the increase in anions (e.g., AG = 16 mEq/L and HCO3- = 5 mEq/L)
(5g) Coexistence of Metabolic Alkalosis and Metabolic Acidosis
Examples: Vomiting causing alkalosis plus bicarbonate-losing diarrhea causing acidosis
May be suspected by acid-base values that are too normal for clinical picture
Pearls
Pulmonary embolus: Mild to moderate respiratory alkalosis is present unless sudden death occurs. The degree of hypoxia often correlates with the size and extent of the pulmonary embolus. pO2 >90 mm Hg when breathing room air virtually excludes a lung problem.
Acute pulmonary edema: Hypoxemia is usual. CO2 is not increased unless the situation is grave.
Asthma: Hypoxia occurs even during a mild episode and increases as the attack becomes worse. As hyperventilation occurs, the pCO2 falls (usually<35 mm Hg); a normal pCO2 (>40 mm Hg) implies impending respiratory failure; increased pCO2 in a true asthmatic (not bronchitis or emphysema) indicates impending disaster and the need to consider intubation and ventilation assistance.
COPD (bronchitis and emphysema) may show two patterns—“pink puffers,” with mild hypoxia and normal pH and pCO2, and “blue bloaters,” with hypoxia and increased pCO2; normal pH suggests compensation and decreased pH suggests decompensation.
Neurologic and neuromuscular disorders (e.g., drug overdose, Guillain-Barré syndrome, myasthenia gravis, trauma, succinylcholine): Acute alveolar hypoven-tilation causes uncompensated respiratory acidosis with high pCO2, low pH, and normal HCO3-. Acidosis appears before significant hypoxemia, and rising CO2 indicates rapid deterioration and need for mechanical assistance.
Sepsis: Unexplained respiratory alkalosis may be the earliest sign of sepsis. It may progress to cause metabolic acidosis, and the mixed picture may produce a normal pH; low HCO3- is useful to recognize this. With deterioration and worsening of metabolic acidosis, the pH falls.
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Salicylate poisoning characteristically shows poor correlation between serum salicylate level and presence or degree of acidemia (because as pH drops from 7.4 to 7.2, the proportion of nonionized to ionized salicylate doubles and the nonionized form leaves the serum and is sequestered in the brain and other organs, where it interferes with function at a cellular level without changing blood levels of glucose, etc.). Salicylate poisoning in adults typically causes respiratory alkalosis, but in children this progresses rapidly to mixed respiratory alkalosis/metabolic acidosis and then to metabolic acidosis (in adults, metabolic acidosis is said to be rare and a near-terminal event).
Isopropyl (rubbing) alcohol poisoning produces enough circulating acetone to produce a positive nitroprusside test (it therefore may be mistaken for diabetic ketoacidosis; thus insulin should not be given until the blood glucose is known). In the absence of a history, positive serum ketone test associated with normal anion gap, normal serum HCO3-, and normal blood glucose suggests rubbing alcohol intoxication.
A change in chloride concentration independent of, or out of proportion to, changes in sodium usually indicates an acid-base disorder.
Nutritional Deficiencies
Copper Deficiency
Copper is a metal component of various enzymes (e.g., cytochrome oxidase, superoxide dismutase, tyrosinase) involved in Hb synthesis, bone and elastic tissue development, and CNS function.
Nutritional Copper Deficiency
Found in patients on parenteral nutrition and in neonates and premature infants and children recovering from severe protein/calorie malnutrition fed iron-fortified milk formula with cane sugar and cottonseed oil.
Anemia not responsive to iron and vitamins
Leukopenia with WBC <5,000/μL and neutropenia (<1,500/μL)
  • Copper administration corrects neutropenia in 3 weeks and anemia responds with reticulocytosis.
Decreased copper and ceruloplasmin in plasma and decreased hepatic copper confirm diagnosis.
“Kinky Hair” (Menkes) Syndrome
Menkes syndrome is an X-linked recessive error of copper metabolism caused by gene mutations that block copper transport from intestinal mucosa cells to blood, causing copper deficiency. It is a syndrome of neonatal hypothermia, feeding difficulties, and sometimes prolonged jaundice; at 2 to 3 months, seizures and progressive hair depigmentation and twisting take place. The syndrome also includes a striking facial appearance, increasing mental deterioration, infections, failure to thrive, death in early infancy and changes in the elastica interna of arteries.
  • Decreased copper in serum and liver; normal in red blood cells (RBCs).
Increased copper in amniotic fluid, cultured fibroblasts, and amniotic cells
Decreased serum ceruloplasmin
Serum Copper Also Decreased In
Wilson disease (total copper is decreased; see Chapter 8): mutation interferes with copper transport from intestinal mucosal cytoplasm to Golgi apparatus, where it becomes bound to protein.
Nephrosis (ceruloplasmin lost in urine)
Acute leukemia in remission
Some iron-deficiency anemias of childhood (that require copper as well as iron therapy)
Kwashiorkor, chronic diarrhea
Adrenocorticotropic hormone and corticosteroids
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Serum Copper Increased In
Wilson disease (free copper is increased; see Chapter 8)
Anemias
  • Pernicious anemia
  • Megaloblastic anemia of pregnancy
  • Iron-deficiency anemia
  • Aplastic anemia
Leukemia and lymphoma
Infection, acute and chronic
Biliary cirrhosis
Hemochromatosis
Collagen diseases (including systemic lupus erythematosus [SLE], rheumatoid arthritis, acute rheumatic fever, glomerulonephritis)
Hypothyroidism
Hyperthyroidism
Frequently associated with increased c-reactive protein (CRP)
Ingestion of oral contraceptives and estrogens
Pregnancy
Zinc Deficiency or Toxicity
Zinc is required for production of functionally mature T cells and for activation of T cells. It is a component of many enzymes, including DNA and RNA polymerases.
Deficiency Caused By
Acrodermatitis enteropathica (rare autosomal recessive disease of infancy due to block in intestinal absorption of zinc)
Inadequate nutrition (e.g., parenteral alimentation)
Excessive requirements
Decreased absorption or availability
Increased losses
Iatrogenic
Plasma concentrations
  • Normal range = 70 to 120 μg/dL
  • Moderate depletion = 40 to 60 μg/dL
  • Severe depletion = 20 μg/dL
No accurate indicators of zinc status. Zinc levels in plasma, RBC, and hair are frequently misleading.
Decreased or very excessive urinary zinc excretion may be helpful.
Toxicity Caused By
Acute: ingestion of >200 mg/d
Chronic: ingestion of >25 mg/d may cause copper deficiency. Ingestion of >150 mg/d may decrease high-density lipoprotein cholesterol (HDL-C).
Failure to Thrive1
In evaluations for failure to thrive, premature infants (shortened gestation period) should be differentiated from infants with weight below that expected for gestational age.
Footnote
1
Stoler JM, Leach NT, Donahoe PK. Case records of the Massachusetts General Hospital. Case 36-2004: A 23-day-old infant with hypospadias and failure to thrive. N Engl J Med 2004;351: 2319–2326.
Intrauterine Growth Retardation
Intrauterine growth retardation refers to low-birth-weight infants who are mature by gestational age.
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Due To
Maternal factors
  • Chronic hypertension, especially with renal involvement and proteinuria
  • Chronic renal disease
  • Severe, long-standing diabetes mellitus
  • Preeclampsia and eclampsia with underlying chronic vascular disease
  • Maternal protein-calorie malnutrition
  • Hypoxia, e.g., cyanotic heart disease, pregnancy at high altitudes, hemoglobinopathies, especially sickle cell disease
  • Alcohol and other drug abuse
Placental conditions
  • Extensive infarction
  • Parabiotic transfusion syndrome
  • Hemangioma of placenta or cord
  • Abnormal cord insertion
Fetal factors
  • Chromosomal abnormalities, especially trisomies of D group and chromosome 18
  • Malformations of GI tract that interfere with swallowing
  • Chronic intrauterine infections (e.g., rubella, cytomegalovirus [CMV], herpes simplex virus, syphilis, toxoplasmosis)
Unexplained
Postnatal Failure to Thrive
Due To
Cause % of Cases
Inadequate caloric intake 87
Maternal (e.g., caloric restriction, child abuse, emotional disorders)
Congenital abnormalities (e.g., cleft lip or palate, tracheoesophageal fistula, esophageal webs, macroglossia, achalasia)
Acquired abnormalities (e.g., esophageal stricture, subdural hematoma, hypoxia, diabetes insipidus)
Decreased intestinal function
Abnormal digestion, e.g.:
   Cystic fibrosis 3.0
   Trypsin deficiency
   Monosaccharidase and disaccharidase deficiencies
Abnormal absorption, e.g.:
   Celiac syndrome 0.5
   Gastroenteritis
   Biliary atresia
   Megacolon
   Giardiasis
   Protein-losing enteropathy
Increased utilization of calories
   Infant of narcotic-addicted mother
   Prolonged fever (e.g., chronic infections)
   Excessive crying
   Congenital heart disease
Renal loss of calories
   Aminoaciduria, e.g.:
   Maple syrup urine disease 0.5
   Methylmalonic academia 0.5
Chronic renal disease, e.g., renal tubular acidosis, pyelonephritis, polycystic disease, congenital/acquired nephritis, congenital nephrosis, nephrogenic diabetes insipidus
Other
   Anemias, e.g., fetal-maternal transfusion, hemoglobinopathies, iron deficiency
   Hypercalcemia, e.g., hyperparathyroidism, vitamin A or D intoxication, idiopathic
   Endocrine
   Hypothyroidism 2.5
   Hypoadrenalism
   Hyposomatotropism
   Congenital hyperthyroidism
Metabolic
   Glycogen storage disease 0.5
   Galactosemia
   Hypophosphatasia
   Mucopolysaccharidosis
   Rickets
CNS lesions
Subdural hematoma 2.5
   Intracerebral hemorrhage
   Tumors
   Unknown
CNS, central nervous system.
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Laboratory Evaluation
Initial
  • Pathologic examination of placenta
  • Complete blood count (CBC) (anemia, hemoglobinopathy)
  • Urine—reducing substances, ferric chloride test, pH, specific gravity, microscopic examination, colony count and culture
  • Stool—occult blood, ova and parasites, pH
  • Serum—sodium, potassium, chloride, bicarbonate, creatinine, calcium, albumin, protein
  • State newborn screening
More detailed tests
  • Sweat chloride and sodium (see section on cystic fibrosis)
  • Serum thyroid-stimulating hormone and T4 (hypothyroidism)
  • Serum and urine amino acids (aminoacidurias) and organic acids
  • Rectal biopsy
  • Serologic tests for congenital infection (HIV, rubella, CMV, toxoplasmosis, syphilis)
  • Duodenal enzyme measurements
  • Chromosome studies (trisomy D, E)
Imaging studies (e.g., GI series, renal ultrasound, brain MRI or CT scan, echocardiography)
Adult Malnutrition and Kwashiorkor
Adult malnutrition and kwashiorkor occur in patients with inadequate protein intake in presence of low caloric intake or normal caloric intake and increased catabolism (e.g., trauma, severe burns, respiratory or renal failure, nonmalignant GI tract disease); they may develop quickly. A major loss of protein from visceral compartments may impair organ function.
  • These laboratory tests all have low sensitivity/specificity (S/S) or may not be easily available.
Decreased serum proteins
  • Albumin has half-life of 21 days (2.8–3.4 mg/dL in mild deficiencies, 2.1–3.0 mg/dL in moderate deficiencies, <2.1 mg/dL in severe deficiencies) is a poor marker for early malnutrition.
  • Prealbumin (transthyretin) is more sensitive than albumin because of its shorter half-life of 1.9 days. Normal range = 18 to 36 mg/dL: severe malnutrition <10.7 mg/dL; moderate malnutrition = 10.7 to 16 mg/dL; is likely to benefit from early therapy. With therapy, increases >1 mg/dL daily. Decreased in renal failure.
  • Retinol-binding protein (carrier for vitamin A) has a half-life of 12 hours; is effective monitor of growth rate in preterm infants. Also decreased in impaired liver function (e.g., hepatitis, cirrhosis, obstructive jaundice), vitamin A deficiency, hyperthyroidism, and some types of amyloidosis. Increased in renal failure.
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  • Transferrin (150–200 mg/dL in mild, 100–150 mg/dL in moderate, <100 mg/dL in severe deficiencies) or total iron-binding capacity. Increase in transferrin caused by inflammation decreases diagnostic utility. Direct measurement is preferred because calculation is affected by iron metabolism and laboratory variability. Poor sensitivity in this condition.
  • CRP rises rapidly during catabolism and declines during anabolism.
  • Other protein markers with short-lives have been suggested, such as fibronectin.
Other chemistry values
  • BUN is decreased.
  • Fluid and electrolyte disorders are common, e.g., hyperchloremic metabolic acidosis, decreased potassium, and decreased phosphate.
Hematologic values
  • Decreased total lymphocyte count evidencing diminished immunologic resistance (normal = 2,000–3,500/μL; <1,500/μL is indication for further assessment; moderate = 800–1,200/μL; severe <800/μL); should always be interpreted with total WBC count.
  • Mild normochromic, normocytic anemia is common.
  • All serum complement components except C4 and sometimes C5 are decreased.
Marasmus
Marasmus is a chronic deficiency in total energy intake, as in wasting illnesses (e.g., cancer) with protein loss from somatic compartment without necessary losses in visceral component.
Serum protein levels are usually normal.
Mild anemia is common.
Immune function is impaired.
Clinically, show severe wasting of skeletal muscle and fat; edema is distinctively absent. May progress to marasmic kwashiorkor.
Laboratory findings due to underlying diseases (e.g., cancer) or complications (e.g., infection).
Monitor Nutritional Therapy
Weekly 24-hour urine nitrogen excretion 1×/week reflects degree of hypermetabolism and correction of deficits.
Increase of serum prealbumin and retinol-binding proteins by 1 mg/dL/day indicates good response. Measure two to three times per week. May precede improvement in albumin levels by 7 to 10 days.
Somatomedin C has also been suggested for monitoring.
Fluid and electrolyte levels should be corrected.
Nutritional Factors in Young Children, Laboratory Indicators
BUN <6 mg/dL or urine <8 mg/g of creatinine suggests recent low protein intake. Serum albumin <3.2 g/dL suggests low protein intake, but this is a rather insensitive nonspecific indicator of protein status.
Iron—see Chapter 11.
Vitamin A—serum carotene <40 μg/dL suggests low intake of carotene. Serum vitamin A <20 μg/dL suggests low stores of vitamin A or may indicate failure of retinol transport out of liver into circulation.
Ascorbic acid—serum ascorbate <0.3 mg/dL suggests recent low intake. Whole blood ascorbate <0.3 mg/dL indicates low intake and reduction in body pool of ascorbic acid. Leukocyte ascorbic acid <20 mg/dL suggests poor nutritional status.
Riboflavin—<250 μg/g of creatinine in urine suggests low recent intake of riboflavin. Glutathione reductase-flavin adenine dinucleotide effect, expressed as ratio >1.2:1, suggests poor nutritional status.
Thiamine—<125 μg/g of creatinine in urine suggests low intake of thiamine. Transketolase–thiamine pyrophosphate effect, expressed as a ratio >1.5:1, suggests poor nutritional status.
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Folate—serum folate <6 μg/dL suggests low intake. RBC folate <20 μg/dL or increased excretion of formiminoglutamic acid (FIGLU) in urine following histidine load suggests poor nutritional status.
Iodine—<50 μg/g of creatinine in urine suggests recent low intake of iodine.
Calcium, phosphorus, alkaline phosphatase (ALP)—rickets (see Chapter 10).
Total Parenteral Nutrition, Metabolic Complications
Decreasing serum prealbumin (transthyretin) level after 2 weeks of total parenteral nutrition (TPN) indicates poor prognosis, but increasing or unchanged level indicates anabolism and protein replenishment and suggests probable survival.
Serum cholesterol decreases rapidly during first 2 days, then remains at low level. Apolipoprotein A (Apo A) decreases 30% to 50% after long-term TPN, but Apo B is usually unchanged.
Hyperglycemia (which may cause osmotic diuresis and hyperosmolarity) or hypoglycemia.
Serum electrolytes are usually unchanged, but sodium may decrease slightly and potassium may increase slightly after fifth day. Changes depend on solution composition and infusion rate. Frequent monitoring is indicated.
Ketosis develops if insufficient calories or low glucose concentration; may indicate onset of infection.
Hyperosmolarity due to TPN infusion.
Lactic or hyperchloremic metabolic acidosis develops in some patients.
Serum creatinine and creatinine clearance are not significantly changed.
Serum uric acid decreases markedly by second to 17th day of TPN and returns to pretreatment level 3 to 7 days after cessation of TPN.
Transiently increased serum AST (3× to 4×), alanine aminotransferase (ALT) (3× to 7×), ALP (2×), and γ-glutamyltransferase (GGT). Direct bilirubin and LD normal or slightly increased. Levels improve 1 week after cessation of TPN and return to normal in 1 to 4 months.
Serum folate falls 50% if not supplemented.
67% of children show eosinophilia (>140/μL) after 9 days of TPN.
Abnormal plasma amino acid levels.
Deficiency of essential fatty acids (on fat-free TPN), zinc, or copper
Laboratory findings of sepsis (e.g., Candida) due to infection of catheter
Some Guidelines for Monitoring Patients on TPN
Twice weekly: chemistry profile, electrolytes, transthyretin
Weekly: CBC, urinalysis, chemistry and acid-base profiles, iron, zinc, copper, magnesium, triglycerides (TG), ammonia
Every 2 weeks: Folate, vitamin B12
Baseline: All of the above tests
Patient with an unstable clinical condition may require testing daily or more often. Fever must always be explained.
Vitamins
Vitamins are essential chemical micronutrients that cannot be synthesized. Fat-soluble vitamins are A, D, E, and K; water-soluble vitamins are C (ascorbic acid) and the B vitamins (see following).
Vitamin A Deficiency
  • Decreased plasma level of retinol vitamin A.
Elevated carotenoids may cause false low values for vitamin A.
Laboratory findings due to preceding conditions (e.g., malabsorption, alcoholism, restricted diet).
Toxicity caused by daily ingestion of >33,000 IU (chronic) or >500,000 IU (acute) may cause hepatocellular necrosis, intracranial hypertension.
Vitamin B1 (Thiamine) Deficiency (Beriberi)
Thiamine deficiency causes inadequate adenosine triphosphate (ATP) synthesis and abnormal carbohydrate metabolism.
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Increased blood pyruvic acid level
  • - Decreased thiamine levels in blood and urine; become normal within 24 hours after therapy begins (thus, baseline levels should be established first).
RBC transketolase <8 IU (baseline), and addition of thiamine pyrophosphate causes >20% increase.
Laboratory findings due to complications (e.g., heart failure)
  • Laboratory findings due to underlying conditions (e.g., renal dialysis, chronic diarrhea, inadequate intake [polished rice], alcoholism)
Vitamin B2 (Riboflavin) Deficiency
Riboflavin is a coenzyme for various biochemical reactions.
  • Decreased riboflavin level in plasma, RBCs, WBCs
  • RBC glutathionine reductase activity decreased in RBCs; not useful in persons with glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Vitamin B3 (Niacin) Deficiency
A deficiency of niacin causes pellagra—dermatitis, dementia, and diarrhea (the “three D’s”).
  • Decreased excretion of niacin metabolites (nicotinamide) in urine
  • Blood niacin level <24 μmol/L is not reliable.
  • Plasma tryptophan level is markedly decreased; also occurs in carcinoid syndrome.
Vitamin B6 (Pyridoxine) Deficiency
  • Decreased serum or RBC levels of vitamin B6.
  • Decreased pyridoxic acid in urine.
  • Measure xanthurenic acid after oral tryptophan load.
Vitamin B12 and Folic Acid Deficiency
Vitamin C Deficiency (Scurvy)
The vitamin C level is measured as the sum of ascorbic and dehydroascorbic acid concentrations.
  • Plasma level of ascorbic acid is decreased; <0.2 mg/dL suggests vitamin C deficiency; usually 0 in frank scurvy. Reflects recent dietary intake. (Normal = 0.5–1.5 mg/dL, but lower level does not prove diagnosis.) Decreased by smoking. Levels are 20% higher in women.
  • Ascorbic acid in buffy coat (WBC) reflects tissue stores, is decreased—usually absent in clinical scurvy. (Normal is 30 mg/dL.) Decreased by smoking.
Ascorbic acid is measured in two 24-hour urine samples; one at baseline and the other 2 days after oral ascorbic acid administration. Vitamin C deficiency is indicated by <50 mg/dL in second specimen.
After protein meal or administration of tyrosine, tyrosyl compounds are present in urine (detected by Millon’s reagent) in patients with scurvy but are absent in normal persons.
Serum ALP is decreased; serum calcium and phosphorus are normal.
Rumpel-Leede test is positive.
Microscopic hematuria is present in one third of patients.
Stool may be positive for occult blood.
Laboratory findings due to associated deficiencies (e.g., anemia caused by folic acid deficiency) are present.
Vitamin D Deficiency or Excess
See Rickets, Chapter 10, and discussion of excess vitamin D in Chapter 13.
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Vitamin E Deficiency
Vitamin E acts as an antioxidant and free radical scavenger, especially in cell membranes.
  • Plasma α-tocopherol <0.4 mg/dL in adults; <0.15 mg/dL in infants age 1 month
Laboratory findings due to underlying conditions (e.g., malabsorption in adults; diet high in polyunsaturated fatty acids in premature infants)
Vitamin K Deficiency
Vitamins, Reference Ranges (Blood)
Reference ranges for vitamins* have limited utility because blood levels may not reflect tissue stores.
Vitamin A
    Retinol 360–1,200 μg/L
<20 μg/dL indicates low intake and tissue stores
20–36 μg/dL is indeterminate
    Retinyl esters ≤1.0 μg/dL
Carotene 48–200 μg/dL
Vitamin C (ascorbic acid) 0.2–2.0 mg/dL
<0.2 mg/dL represents deficiency
Vitamin D Indirect estimate by measuring serum ALP, calcium, and phosphorus
    Total 25-hydroxy vitamin D 14–42 ng/mL (winter)
15–80 ng/mL (summer)
    1,25-dihydroxy vitamin D 15–60 pg/mL
Vitamin E (alpha-tocopherol)
    Children 3.0–15.0 μg/mL
    Adults 5.5–17.0 μg/mL
    Deficiency <3.0 μg/mL
    Excess >40 μg/mL
Vitamin B1 (thiamine) 5.3–7.9 μg/dL
Vitamin B2 (riboflavin) 3.7–13.7 μg/dL
Vitamin B12 (cobalamin)
    Low <150 pg/mL
    Normal 190–900 pg/mL
Unsaturated vitamin B12-binding capacity 870–1,800 pg/mL
Folate
Serum Usual normal range is 5–15 ng/mL; is associated with normal hematologic findings.
3–5 ng/mL is borderline; is associated with variable hematologic findings.
<3 ng/mL is associated with positive hematologic findings.
RBC
    <1 y old 74–995 ng/mL
    1–11 y old 96–362 ng/mL
    ≥12 y old 180–600 ng/mL
ALP, alkaline phosphatase.
Table 12-8. Serum Markers in Detection of Various Prenatal Conditions
Condition AFP hCG Unconjugated Estriol Detection Rate
Anencephaly 4+ 95%
Open spina bifida 3+ 80%
Abdominal wall defects 3+ 75%
Trisomy 21 (Down syndrome) D I D 60%
Trisomy 18 DD DD DD 60%
Other chromosomal abnormalities I/D I/D I/D 50%
D = decreased; DD = strongly decreased; I = increased; I/D = increased or decreased.
Source: Wasserman ER. Preventing problem pregnancies. Advance/Laboratory Nov 1997:53.
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Inherited Metabolic Disorders
Laboratory Tests For Prenatal Screening and Diagnosis2
Footnote
2
Donnenfeld AE, Lamb AN. Cytogenetics and molecular cytogenetics in prenatal diagnosis. Clin Lab Med 2003;23:457–480.
Use
General Risk Factors:
  • Maternal age ≥35 years at delivery
  • Abnormal maternal serum α-fetoprotein (AFP), human chorionic gonadotropin (hCG), or unconjugated estriol
Ethnic Risk Factors:
  • Sickle cell anemia (presence of sickling; confirmed by Hb electrophoresis)
  • Tay-Sachs disease (decreased serum hexosaminidase A)
  • α- and β-thalassemia (decreased mean corpuscular volume; confirmed by Hb electrophoresis)
Specific Risk Factors:
  • Rubella, toxoplasmosis, or CMV infection
  • Maternal disorder (e.g., diabetes mellitus, phenylketonuria [PKU])
  • Teratogen exposure (e.g., radiation, alcohol, isotretinoin, anticonvulsants, lithium)
  • Previous stillbirth or neonatal death
  • Previous child with chromosomal abnormality or structural defect
  • Inherited disorders (e.g., cystic fibrosis, metabolic disorders, sex-linked recessive disorders)
  • Either parent with balanced translocation or structural abnormality
Maternal Serum Sampling
See AFP in open neural tube, anencephaly, ventral wall defects, etc.
See trisomy 21 (Down syndrome) and trisomy 18.
Fetal DNA in maternal serum has been reported for diagnosis of fetal Rh(D) status, β-thalassemia, myotonic dystrophy, achondrodysplasia, trisomy 21, and preeclampsia.3
Footnote
3
Lo YM, Tein MS, Lau TK, et al. Quantitative analysis of fetal DNA in maternal plasma and serum: implications for noninvasive prenatal diagnosis. Am J Hum Genet 1998;62:768–775.
Fig. 12-4. Algorithm for α-fetoprotein (AFP) testing in pregnancy (detects virtually all cases of anencephaly and 80% of cases of open spina bifida, with very few false-positive results).
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Amniocentesis
Generally not done before 14 weeks of gestation. Risk of fetal loss ∼0.5%.
Cell culture takes 5 to 7 days; activity similar to that in fibroblasts.
Use
In women >35 years old to detect various chromosomal abnormalities.
Can detect intermediary metabolites of some inborn errors, especially organic acid disorders.
Confirm abnormal maternal serum findings, e.g., AFP, hCG.
Chorionic Villus Sampling4
Generally done between 10 to 13 weeks of gestation; sometimes as early as 6 to 7 weeks. Risk of fetal loss is ≤2%. Failure to obtain results = 2%.
Contamination with maternal decidua must be avoided for accurate diagnosis based on fetal chromosomes, enzyme assay, or DNA analysis.
In some patient populations, a negative culture for Neisseria gonorrhoeae or herpes simplex virus may be required.
Associated with ∼7% fetal loss similar to amniocentesis (spontaneous rate ∼4.5%).
False-positive result in 2% of cases compared with 0.3% of cases using amniocentesis.
Most prenatal diagnoses of enzyme defects are now made with this assay.
Does not include biochemical analysis of amniotic fluid (AF) (e.g., AFP, others). Therefore cannot test for neural tube defects.
Primary advantage is to provide earlier results than AF, allowing pregnancy termination in first trimester or relieving anxiety.
Both parents carry recessive gene (e.g., sickle cell anemia, cystic fibrosis, Tay-Sachs).
X-linked recessive gene (e.g., hemophilia, Duchenne muscular dystrophy).
Not reliable for diagnosis of Fragile X syndrome.
Footnote
4
Cole HM (Ed.) Chorionic villus sampling: a reassessment. Diagnostic and therapeutic technology assessment. JAMA 1990;263:305.
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Indications
Chromosomal examination:
  • 80% for trisomies 21, 18, 13; aneuploidies or mosaicism involving sex chromosomes
  • 20% unbalanced translocations or deletions, others.
  • Previous child with chromosomal trisomy
  • Mother carrier of X-linked disorder (to determine fetal sex)
  • Parent carrier of chromosomal translocation
  • Maternal age >35
Restriction enzyme assay:
  • Hemoglobinopathy (e.g., thalassemia)
  • Lesch-Nyhan syndrome
  • α1-antitrypsin deficiency
  • PKU
Metabolic assay:
  • Adenosine deaminase deficiency
  • Adrenoleukodystrophy
  • Argininosuccinic aciduria
  • Citrullinemia
  • Cystinosis
  • Fabry disease
  • Fanconi anemia
  • Farber disease
  • Gaucher disease
  • Gm1 gangliosidosis
  • Gm2 gangliosidosis (Tay-Sachs disease)
  • Homocystinuria
  • Krabbe disease
  • Lesch-Nyhan syndrome
  • Maple syrup urine disease
  • Menkes syndrome
  • Metachromatic leukodystrophy
  • Methylmalonic acidemia
  • Mucolipidosis II (I-cell disease)
  • Mucopolysaccharidosis (Ia, II, III, IV)
  • Multiple sulfatase deficiency
  • Niemann-Pick disease
  • Pompe disease
  • Wolman disease
  • Zellweger syndrome
Fetal Blood Sampling
Generally done ∼15th week but usually also successful between 18 and 23 weeks. Check for maternal serum contamination by determining hCG concentration. Additional risk to fetus of 2%.
Use
Prenatal diagnosis of
  • RBC isoimmunization, e.g., rhesus factor, minor antigens
  • Alloimmune or autoimmune thrombocytopenia
  • Hemoglobinopathies (e.g., thalassemias, sickle cell disorders, spherocytosis, enzyme deficiencies [e.g., G6PD])
  • Coagulation defects (e.g., Factor VIII and IX hemophilias and fetal sex, other factor deficiencies, von Willebrand disease)
  • Immune-deficiency disorders (e.g., severe combined immunodeficiency, Wiskott-Aldrich syndrome, ataxia telangiectasia, chronic granulomatous disease, homozygous C3 deficiency, Chédiak-Higashi syndrome)
  • Intrauterine infections (e.g., rubella, toxoplasmosis, varicella, CMV, parvovirus B19) to determine specific IgM and increased total IgM, increased WBC and eosinophil count, decreased platelet count, various blood chemistries
  • Chromosomal disorders (e.g., mosaicism, Fragile X)
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  • Metabolic and cytogenetic disorders (e.g., phenylketonuria, α1-antitrypsin deficiency, cystic fibrosis, Duchenne muscular dystrophy)
  • Others (e.g., familial hypercholesterolemia, hyperphenylalaninemia, adrenoleukodystrophy)
  • Fetal acid-base balance and metabolic state
  • Fetal drug administration
Fetal Biopsy
Use
Liver biopsy for diagnosis of deficiency of long chain 3-hydroxyacyl-CoA dehydrogenase, ornithine transcarbamylase deficiency, atypical PKU due to deficiency of glutamyl transpeptidase cyclohydrolase I, type I hyperoxaluria, GSD type I.
Skin biopsy, e.g., certain severe genetic disorders such as epidermolysis bullosa
Muscle biopsy for Duchenne muscular dystrophy
Fetal Urine
Use
In cases of oligohydramnios when AF cannot be obtained.
To diagnose and treat fetal obstructive uropathy.
Cystic Hygroma Fluid
Use
To diagnose associated chromosomal abnormalities (e.g., 45 X, trisomy 21, trisomy 18).
Genetic Testing
Use
Carrier identification (e.g., Tay-Sachs disease, sickle cell trait)
Prenatal diagnosis (e.g., Down syndrome)
Newborn screening (e.g., PKU, congenital hypothyroidism)
Ultrasound and Echocardiography
Use
To guide sampling techniques.
To verify gestational age.
Karyotyping is done if malformations are found, since one third of these fetuses will have a chromosomal disorder.
Nuchal thickness and nasal bone absence for prenatal diagnosis of trisomy 21.
May be abnormal in trisomy 13, 18, 21, and 45X and triploidy.
Detection of ∼50% of major heart, kidney, and bladder abnormalities, which are not detected by maternal serum AFP screening.
Karyotype Analysis
Use
Determine status of chromosomes X, Y, 21, 18, and 13.
Molecular Diagnosis
Use
Direct detection of gene deletions and mutations and linkage analysis using cultured amniocytes or chorionic villi can make some diagnoses, even when gene products are not present (e.g., adult polycystic kidney disease, sickle cell disease, α-thalassemia, cystic fibrosis, Gaucher disease, Duchenne muscular dystrophy, fragile X syndrome, factor deficiencies).
Isolation of Fetal Cells in Maternal Blood or Fetal DNA
Usual ratio of fetal cells to maternal cells = 1:1,000 to 1:5,000.
Use
Allows diagnosis by flow cytometry and polymerase chain reaction (PCR). PCR can demonstrate a Y chromosome in women carrying male fetuses.
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Laboratory Tests For Newborn Screening5
Footnote
5
Waisbren SE. Newborn screening for metabolic disorders. JAMA 2006;296:993.
Nuclear Sexing (Sex Chromatin; Barr Bodies)
In nuclear sexing, epithelial cells from a buccal smear (or vaginal smear, etc.) are stained with cresyl violet and examined microscopically. A dense body (Barr body) on the nuclear membrane represents one of the X chromosomes and occurs in 30% to 60% of female somatic cells. The maximum number of Barr bodies is 1 less than the number of X chromosomes.
Largely replaced by chromosome analysis. A normal count does not rule out chromosomal abnormalities.
If there are <10% of cells containing Barr bodies in a patient with female genitalia, karyotyping should be done to delineate probable chromosomal abnormalities.
No Barr bodies in:
  • Normal males
  • Turner syndrome (ovarian dysgenesis)
Two Barr bodies may be found in:
  • 47 XXX female
  • 48 XXXY male (Klinefelter syndrome)
  • 49 XXXYY male (Klinefelter syndrome)
Three Barr bodies may be found in:
  • 49 XXXXY male (Klinefelter syndrome)
Are same as drumstick nuclear appendages in 2% to 3% of leukocytes in normal females and indicate the presence of two X chromosomes in the karyotype. It is not found in males. There is a lower incidence of drumsticks in Klinefelter syndrome (XXY) as opposed to the extra Barr body. (Mean lobe counts of neutrophils are also decreased.)
Incidence of drumsticks is decreased and mean lobe counts are lower also in trisomy 21.
Double drumsticks are exceedingly rare and diagnostically impractical.
Chromosome Analysis (Karyotyping)
Every nucleated human cell contains a complete genome of 6 × 109 base pairs of DNA packed into 46 chromosomes consisting of 22 pairs of autosomes and one pair of sex chromosomes (XX in females, XY in males). Cytogenic disorders are present in ≥1% of live births, <50% of spontaneous fetal losses.
Use
Suspected autosomal syndromes:
Down (trisomy 21), trisomy 18, trisomy 13, Cri du chat syndrome
Suspected sex-chromosome syndromes:
Klinefelter XXY, XXXY
  • Turner XO
  • “Superfemale” XXX, XXXX
  • “Supermale” XYY
  • “Funny-looking kid” syndromes, especially with multiple anomalies, including mental retardation and low birth weight
  • Possible myelogenous leukemia to demonstrate Philadelphia chromosome
  • Ambiguous genitalia
  • Infertility (some patients)
  • Repeated miscarriages
  • Primary amenorrhea or oligomenorrhea
  • Mental retardation with sex anomalies
  • Hypogonadism
  • Delayed puberty or abnormal development at puberty
  • Disturbances of somatic growth
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Newborn Screening6,7,8
Footnotes
6
Chace DH, Kalas TA, Naylor EW. Use of tandem mass spectrometry for multianalyte screening of dried blood specimens from newborns. Clin Chem 2003;49:1797–1817.
Use
Genetic tests are available for >940 diseases, of which 400 are only research tests.
The most current methodology employs tandem mass spectrometry (MS/MS), which can detect >50 genetic disorders.
Amino acids that can be measured include glycine, alanine, histidine, glutamic acid, glutamine, arginine, and ornithine.
Can also detect carnitine, acylcarnitines, fatty acids, methylmalonic academia, propionic acidemia, various cobalamin defects, and vitamin B12 deficiency.
Patterns rather than only single metabolites are significant.
Ideally, to screen for disorders that are asymptomatic, can cause irreversible damage, and for which there is effective treatment.
Population prevalence sufficient to limit false-positive and false-negative results.
High cost:benefit ratio.
Adequate follow-up to assure appropriate treatment.
Neonatal Screening, Disorders and Incidence
Disorder Incidence
Phenylketonuria and its milder variations Among Caucasians, between 1:10,000 and 1:25,000; 1 in 50 persons is a carrier
Iminoglycinuria 1:10,000
Cystinuria 1:7,000
Histidinemia 1:14,000–1:20,000 live births in
United States and 1:8,000 in Japan
Hartnup disease 1:30,000
Genetic mucopolysaccharidoses 1:25,000
Galactosemia
    Galactokinase deficiency 1:150,000
    Classic galactose-1-phosphate uridyltransferase 1:60,000
    Uridinediphosphate-galactose-4- epimerase <1:50,000
Argininosuccinic acidemia 1:100,000
Cystathioninemia 1:100,000
Hyperglycinemia (nonketotic) 1:150,000
Fanconi syndrome (renal) 1:150,000
Propionic acidemia 1:50,000
Hyperlysinemia <1:300,000
Hyperornithinemia <1:300,000
Hyperprolinemia <1:300,000
Maple syrup urine disease 1:250,000–1:400,000
Homocystinuria 1:50,000–1:150,000
Tyrosinemia 1:40,000–1:50,000
Hypothyroidism 1:3,600–1:4,800
Cystic fibrosis of pancreas 1:2,400 in United States and Western Europe; 1:90,000 in native Hawaiians
Congenital adrenal hyperplasia (90% are of 21-hydroxylase type) 1:67,000 in Maryland; 1:490 in Ypik Eskimos of Alaska
Some Laboratory Clues to Metabolic Diseases in Infants and Children
Various genetic metabolic diseases are so often associated with certain laboratory findings that such clues should alert the physician to rule them out.
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Hypoglycemia:
  • Galactosemia
  • GSDs (IA, IB, III, VI, IX A, B, C)
  • Hereditary fructose intolerance
  • Organic acidemias (e.g., maple syrup urine disease, propionic acidemia, methylmalonic acidemia, isovaleric acidemia, glutaric acidemia, etc.)
  • Tyrosinemia
  • Biotinidase deficiency
  • Endocrine disorders (e.g., adrenal insufficiency, diabetic mother, hypopituitarism.)
  • Others (e.g., Reye syndrome, sepsis, liver disease, drugs.)
Ketosis (massive ketosis, especially in the presence of severe vomiting, is otherwise rare in neonates, even in juvenile diabetes):
  • Galactosemia
  • Hereditary fructose intolerance
  • Maple syrup urine disease
  • Organic acidemias
Acidosis
Amino acid disorders:
  • Maple sugar urine disease
  • Hypervalinemia
  • Hyperleucine-isoleucinemia
Organic acid defects:
  • Isovaleric acidemia
  • Propionic acidemia
  • Methylmalonic acidemia
  • Glutaric acidemia
  • Combined carboxylase deficiency
  • 3-Hydroxy-3-methylglutaric acidemia
  • 2-Methyl-3-hydroxybutyric acidemia
  • Acyl CoA dehydrogenase deficiencies
Glycogen storage diseases:
  • Type Ia
  • Type III
Hyperammonemia
(May be associated with failure to thrive, low birth weight, strong body odor, decreased albumin and calcium, etc.). (Plasma ammonia should be determined in any neonate with unexplained neurologic deterioration or any patient with unexplained encephalopathy or episodic lethargy and vomiting.) Marked hyperammonemia without significant acidosis suggests a urea cycle disorder; should perform serum amino acid assay by High-performance liquid chromatography (HPLC) and urine organic acid assay by GC/MS.
Defects in urea cycle: severe hyperammonemia with respiratory alkalosis:
  • Arginosuccinate synthetase deficiency
  • Arginosuccinate lyases deficiency
  • Arginase deficiency
  • Ornithine transcarbamylase deficiency
  • N-Acetylglutamate synthetase deficiency
  • Carbamyl phosphate synthetase deficiency
Organic acid defects: mild to moderate hyperammonemia (≥500 mg/dL):
  • Methylmalonic acidemia
  • Isovaleric acidemia*
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  • Multiple carboxylase deficiency*
  • Propionic acidemia*
  • Glutaric acidemia type I and II
  • Ketothiolase deficiency
Disorders of dibasic amino acid transport (e.g., hyperornithinemia)
Fatty acid oxidation defects
Transient hyperammonemia of newborn
Reye syndrome
Hepatic failure
Drugs (e.g., valproate)
Increased serum indirect bilirubin:
  • Inborn errors of RBC metabolism (e.g., pyruvate-kinase deficiency or G6PD deficiency)
  • Crigler-Najjar syndrome
  • Gilbert syndrome
  • Hypothyroidism
Increased serum direct bilirubin:
  • Rotor syndrome
  • Dubin-Johnson syndrome
  • Galactosemia
  • Hereditary fructose intolerance
  • α1-antitrypsin deficiency
Hepatomegaly is prominent in:
  • Lysosomal storage diseases, (e.g., mucopolysaccharidoses, mucolipidoses, glycoprotein storage diseases, gangliosidosis)
  • Lipidoses (e.g., Gaucher disease, Niemann-Pick disease, Wolman disease)
  • Disorders of carbohydrate metabolism (e.g., galactosemia, hereditary fructose intolerance, GSDs)
  • Tyrosinemia
  • α1-antitrypsin deficiency
Feeding difficulties or vomiting are associated with many metabolic diseases but are most prominent with:
  • Protein intolerance (e.g., organic acidemias or hyperammonemia syndromes)
  • Carbohydrate intolerance (e.g., hereditary fructose intolerance)
  • Adrenogenital syndrome
Seizures:
  • Glycogen storage disease (hypoglycemia)
  • Galactosemia
  • Fructose intolerance
  • Maple syrup urine disease
  • Congenital lactic acidosis
  • Vitamin D–resistant rickets
  • Organic acidemias
  • Urea cycle disorders
  • Hyperglycemia
  • Pyridoxine dependency
Some Laboratory Clues to Acute Neonatal Illness
Thrombocytopenia
Anemia
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Hypoglycemia
Metabolic acidosis
Hyperammonemia
Classification of Inherited Metabolic Conditions (Abbreviated)
Inherited metabolic conditions are classified according to involved metabolic pathway (e.g., carbohydrate, amino acid, fatty acids), involved cell organelles (e.g., lysosomes, mitochondria), and/or phenotypes.
Disorder Deficiency Substances Detected
Disorders of carbohydrate metabolism
Diabetes mellitus See Chapter 13 Glucose
Pentosuria   L-xylulose
Fructose   Fructose
    Fructosuria Fructose 1–6 phosphate aldolase B deficiency (hereditary fructose intolerance)  
  Fructose 1–6 diphosphatase deficiency  
  Essential fructosuria (hepatic fructokinase deficiency)  
Lactose Familial lactose intolerance Lactose
Galactose   Galactose
    Galactosemia Galactose-1-phosphate uridyltransferase  
  Galactokinase deficiency  
  Galactose-4-epimase deficiency  
Glycogen storage diseases
Disorders of amino acid and organic acid metabolisma
Hyperphenylalaninemia Phenylalanine hydroxylase Phenylalanine (B) and its metabolites (phenylpyruvic acid, ortho-hydroxyphenylacetic acid) in blood, urine and CSF; tyrosine and the derivative catecholamines are deficient.
  Type I (phenylketonuria) Mental retardation
  Type II Milder form of type I
  Type III Transient
Tyrosinemia I Fumarylacetoacetate and maleylacetoacetate hydrolases Succinylacetone, tyrosine (U)
Tyrosinemia II Tyrosine aminotransferase Tyrosine (B, U)
Alkaptonuria Homogentisic acid oxidase Homogentisic acid (U)
Histidinemia Histidase
Homocystinuria Cystathionine synthase Homocystine and methionine (B, U); D cysteine (B)
  Cobalamin metabolism (see “Megaloblastic Anemia,” Chapter 11) Homocystine and methylmalonic acid (B, U), cystathionine (U)
  Methylenetetra-hydrofolate reductase Homocystine (B, U), cystathionine (U)
Hyperlysinemia
    Persistent Lysine ketoglutarate reductase Lysine (B,U)
    Periodic Lysine dehydrogenase Lysine (B) ammonia (B)
Citrullinemia Argininosuccinate synthetase Argininosuccinic acid
Hyperargininemia Arginase
Argininosuccinic aciduria Argininosuccinate (B, U) Citrulline
Hyperammonemias
    Ornithine carbamoylsynthase deficiency Ammonia (B), orotic acid (U); D citrulline  
    Carbamyl phosphate synthetase deficiency Ammonia (B), orotic acid (U); citrulline (B)  
    N-acetylglutamate synthetase deficiency Ammonia (B)  
Maple syrup urine disease (branched-chain ketoaciduria) Branched-chain ketoacid dehydrogenase Leucine, isoleucine, valine, branched-chain ketoacids (B, U)
Isovaleric acidemia Isovaleryl-CoA dehydrogenase Isovaleric acid (B), hydroxyisovaleric acid (U), isovalerylglycine (U)
Glutaric aciduria Glutaryl-CoA dehydrogenase Accumulation of glutaric acid and its metabolites (glutaconic acid and 3-hydroxyglutaric acid)
Nonketotic hyperglycinemia Glycine cleavage system Glycine (B, U, CSF)
Propionic acidemia Propionyl-CoA carboxylase  
Methylmalonic acidemia Methylmalonyl-CoA mutase, adenosylcobalamin synthesis  
Imino acids
Hyperprolinemia Proline oxidase Proline (B, U), glycine (U), hydroxyproline (U)
Hyperhydroxyprolinemia Pyrroline-5-carboxylate dehydrogenase Proline (B, U), glycine (U), hydroxyproline (U), pyrroline-5-carboxylate (U)
Hyperimidodipeptiduria Prolidase (peptidase) Imidodipeptides (U)
Urea cycle disorders
Phenylketonuria Phenylalanine hydroxylase Phenylalanine and its metabolites (phenylpyruvic acid, ortho-hydroxyphenylacetic acid) in B, U, CSF; tyrosine and the derivative catecholamines are deficient
Citrullinemia Argininosuccinic acid synthetase Argininosuccinic acid
Argininemia Arginase  
Argininosuccinic aciduria Argininosuccinate lyase Citrulline
Ornithine carbamoyl-transferase deficiency
N-acetylglutamate synthetase deficiency
Carbamyl phosphate synthetase deficiency
Disorders of proline and hydroxyproline metabolism
Hyperprolinemia I Proline oxidase Proline
Hyperprolinemia II Pyrroline-5-carbgoxylate dehydrogenase Proline
Hyperimidodipeptiduria Prolidase  
HHH syndrome Hyperornithinemia, Hyperammonemia, Homocitrullinuria)  
Organic acid disorders/organic acidurias
Biotinidase deficiency (one cause of multiple carboxylase deficiency)
Cobalamin C defect
Pyruvate and lactate metabolism Lactate dehydrogenase deficiency
Pyruvate dehydrogenase deficiency
Pyruvate carboxylase deficiency
Phosphoenolpyruvate carboxykinase deficiency
 
Branched-chain organic acidemias
Isovaleric acidemia Isovaleryl-CoA dehydrogenase Isovaleric acid (B), hydroxyisovaleric acid (U), isovalerylglycine (U)
Mevalonic acidemia Mevalonate Leucine, isoleucine, valine, branched chain ketoacids (B, U)
Maple syrup urine disease (branched-chain ketoaciduria) Branched-chain ketoacid dehydrogenase  
Organic acid disorders
Propionate and methylmalonate metabolism
    Propionic acidemia Propionyl-CoA carboxylase  
    Methylmalonic acidemia Methylmalonyl-CoA mutase, adenosylcobalamin synthesis  
    Multiple carboxylase deficiency Holocarboxylase synthetase, biotinidase  
Other organic acid disorders
Alkaptonuria (see Chapter 8) Homogentisic acid oxidase  
Hyperoxaluria type I (glycolic aciduria) Alanine:glyoxylate aminotransferase Glycolic and oxalic acid
Hyperoxaluria type II (glyceric aciduria) Glyceric dehydrogenase
Glycerol kinase deficiency
 
Canavan disease Aspartoacylase  
Lysosomal storage disorders
Metachromatic leukodystrophy Arylsulfatase A  
Multiple sulfatase deficiency Multiple lysosomal  
Niemann-Pick disease Sphingomyelinase  
Farber disease Ceramidase  
Gaucher disease Glucocerebrosidase  
Pompe disease (GSD II) α-1,4-glucosidase deficiency  
Krabbe disease Galactocerebrosidase  
Fabry disease α-galactosidase  
Gm1 gangliosidosis β-galactosidase  
Wolman disease Acid lipase  
Cholesteryl ester storage disease Acid lipase  
Mucolipidosis type IV    
Acylcarnitine Disorders
Fatty acid oxidation disorders e.g., Carnitine transporter defects; medium, short, long, and very-long-chain Acyl-CoA dehydrogenase deficiencies; others Various
Peroxisomal disorders
Acatalasia Catalase  
Refsum disease Phytanic acid hydroxylase Various, e.g., very-long-chain fatty acids
Zellweger syndrome Peroxisome biogenesis  
Purine and pyrimidine metabolism disorders
Lesch-Nyhan syndrome Hypoxanthine phosphoribosyltransferase Increased uric acid (B)
Orotic aciduria (see Chapter 11) Uridine-5′-monophosphate synthase Increased orotic acid (B)
Xanthinuria Xanthine oxidase Decreased uric acid (B, U)
Disorders of metal metabolism
Wilson disease (see Chapter 8)
Hemochromatosis
Menkes syndrome
Disorders of lipid metabolism (see Table 12-9)
Disorders of heme proteins
Porphyrinurias
Bilirubin metabolism
Crigler-Najjar syndromes I, II
Gilbert’s disease
Dubin-Johnson syndrome
Rotor syndrome
See Chapter 8  
Membrane transport disorders
Cystinuria    
Hartnup disease    
Iminoglycinuria   Proline, hydroxyproline, glycine (all N or D)
Disorders of serum enzymes
Hypophosphatasia
Hyperphosphatasia
α1-antitrypsin deficiency
Alkaline phosphatase Alkaline phosphatase (D)
Disorders of plasma proteins
Analbuminemia
Agammaglobulinemia
Atransferrinemia
   
Disorders of blood
Coagulation diseases (e.g., hemophilias) See Chapter 11  
RBC G6PD deficiency See Chapter 11  
Hemoglobinopathies (including sickle cell disease and α- and β- thalassemias) See Chapter 11  
Hereditary spherocytosis See Chapter 11  
Hereditary nonspherocytic hemolytic anemia See Chapter 11  
Endocrine disorders
Neonatal hypothyroidism See Fig 13-7  
Congenital adrenal hyperplasia See Chapter 13  
Infectious diseases, (transmitted) e.g.:
HIV, toxoplasmosis See Chapter 15  
Hepatitis B, C See Chapter 8  
Others
Cystic fibrosis See Chapter 8  
Duchenne muscular dystrophy See Chapter 10  
D, decreased; I, increased; N, normal; B, blood; U, urine; CSF, cerebrospinal fluid; GSD, glycogen storage disease; G6PD, glucose-6-phosphate dehydrogenase.
aStern HJ, Finkelstein JD. Heritable diseases of amino-acid metabolism. In: Becker KL, ed. Principles and Practice of Endocrinology and Metabolism. 3rd ed. Philadelphia: Lippincott Williams & Wilkins; 2001; also Wapner RS. In McMillan J, Feigin RD, DeAngelis C, Jones DJ, eds. Inborn Errors of Metabolism; Oski’s Pediatrics. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2006.
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Tests of Lipid Metabolism
Disorders of Lipid Metabolism
Acid Lipase Deficiencies
Acid lipase deficiencies are characterized by the inability to hydrolyze lysosomal TG and cholesteryl esters.
  • Decreased acid lipase in lymphocytes or fibroblasts. Increased serum TG, LDL-C, and cholesterol esters.
Wolman Disease
Wolman disease is a rare autosomal recessive absence of enzyme A of lysosomal acid lipase activity, causing accumulation of total cholesterol (TC) and TG throughout body tissues; death occurs within the first 6 months of life.
Prominent anemia develops by 6 weeks of age.
Peripheral blood smear shows prominent vacuolation (in nucleus and cytoplasm) of leukocytes.
  • Characteristic foam cells in bone marrow resemble those in Niemann-Pick disease.
  • Abnormal accumulation of cholesterol esters and TGs in tissue biopsy (e.g., liver) establishes the diagnosis.
  • Assay shows absent acid lipase activity in many tissues, including leukocytes and cultured fibroblasts. Heterozygotes have enzyme activity of ∼50% of normal in leukocytes or cultured fibroblasts.
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  • Prenatal diagnosis by demonstrating enzyme deficiency in cultured amniocytes.
Laboratory findings due organ involvement:
  • Abnormal liver function tests (caused by lipid accumulation)
  • Malabsorption
  • Decreased adrenal cortical function (diffuse calcification on CT scan).
Cholesteryl Ester Storage Disease
This is a rare, inherited, marked deficiency of isoenzyme A of lysosomal acid lipase activity, causing accumulation of cholesterol ester.
Similar to Wolman disease but is less severe, lacks intestinal malabsorption, and deposits are predominantly cholesterol esters in lysosomes.
Metabolic Syndrome (Syndrome X)9
Metabolic syndrome is a recently recognized constellation of findings, possibly caused by insulin resistance, including hypertension, abdominal obesity, and prothrombotic and proinflammatory states.
Glucose intolerance with fasting blood glucose 110 to 125 mg/dL
Atherogenic dyslipidemia (TG >150 mg/dL, HDL-C <40 mg/dL in men and <50 mg/dL in women, small dense LDL particles
Abnormalities in fibrinolysis and coagulation
Exclusion of other causes of dyslipidemia (e.g., cholestasis, hypothyroidism, chronic renal failure, nephrotic syndrome)
Footnote
9
Reaven GM. The metabolic syndrome: requiescat in pace. Clin Chem 2005;51:931.
Hyperlipidemias, Primary
See Table 12-9. See also Chapter 5.
Hyperalphalipoproteinemia (HDL-C Excess)
Hyperalphalipoproteinemia is inherited as a simple autosomal dominant trait in families with longevity, or it may be caused by alcoholism, extensive exposure to chlorinated hydrocarbon pesticides, or exogenous estrogen supplementation.
Occurs in 1 in 20 adults with mildly increased TC levels (240–300 mg/dL) secondary to increased HDL-C (>70 mg/dL). LDL-C is not increased, TG is normal.
  • Hyperalphalipoproteinemia (HDL-C excess)
    • 1 in 20 adults with mild increased TC levels (240–300 mg/dL) secondary to increased HDL-C (>70 mg/dL)
    • LDL-C is not increased
    • TG is normal
  • Hypobetalipoproteinemia (see Table 13-6)
Severe Hypertriglyceridemia (Type I) (Familial Hyperchylomicronemia Syndrome)
Hypertriglyceridemia is a rare autosomal recessive trait due to deficiency of lipoprotein lipase (LPL) or Apo C-II or circulating inhibitor of LPL. There is marked heterogeneity in causative molecular defects.
Persistent very high TG (>1,000 mg/dL) with marked increase in very-low-density lipoprotein (VLDL) and chylomicrons.
Responds to marked dietary fat restriction.
Patients with Apo C-II deficiency cannot activate LPL in vitro. Deficiency of Apo C-II is shown by isoelectric focusing or two-dimensional gel electrophoresis of plasma.
Associated with recurrent pancreatitis rather than coronary artery disease (CAD).
Laboratory changes due to fatty liver (increased serum transaminase).
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Familial Hypercholesterolemia (Type II)
Familial hypercholesterolemia is inherited as an autosomal dominant disorder.
  • LDL receptors in fibroblasts or mononuclear blood cells are <25% in homozygous and 50% of normal levels in heterozygous patients (performed at specialized labs).
Homozygous—very rare condition (1 per million) in which serum TC is very high (600–1,000 mg/dL) with corresponding increase in LDL. Both parents are heterozygous. Clinical manifestations of increased TC (xanthomata, corneal arcus, CAD that causes death usually before age 30 years).
  • • Neonatal diagnosis requires finding increased LDL-C in cord blood; serum TC is unreliable. Because of marked variation in serum TC levels during the first year of life, diagnosis should be deferred until 1 year of age.
  • • Prenatal diagnosis of homozygous fetus can be made by estimation of binding sites on fibroblasts cultured from amniotic fluids; useful when both parents are heterozygous.
Heterozygous—increased serum TC (300–500 mg/dL) and LDL (two to three times normal) with similar change in a parent or first-degree relative; serum TG and VLDL are normal in 90% and slightly increased in 10% of these cases. Gene frequency occurs 1 in 500 in the general population, but 5% in survivors of acute myocardial infarction (AMI) <60 years old. Premature CAD, tendinous xanthomas, and corneal arcus are often present.
Plasma TG is normal in type II-A but increased in type II-B. This is not the most common cause of phenotype II-A.
Polygenic Hypercholesterolemia (Type IIA)
Polygenic hypercholesterolemia can be diagnosed only after secondary causes of hypercholesterolemia and autosomal dominant traits have been excluded.
Persistent TC elevation (>240 mg/dL) and increased LDL without familial hypercholesterolemia or familial combined hypercholesterolemia. In Type IIB, both LDL and VLDL are increased.
Premature CAD occurs later in life than with familial combined hyperlipidemia.
Xanthomas are rare.
Familial Combined Hyperlipidemia (Types IIB, IV, V)
Familial combined hyperlipidemia occurs in 0.5% of general population and 15% of survivors of AMI <60 years old.
There may be any combination of increased LDL-C and VLDL and chylomicrons; HDL-C is often low; different family members may have increased serum TC or TG or both.
Premature CAD occurs later in life (after age 30 years) than with familial hypercholesterolemia.
Xanthomas are rare.
Patients are often overweight.
Familial Dysbetalipoproteinemia (Type III)
Familial dysbetalipoproteinemia occurs in 1 per 5,000 to 10,000 persons.
Abnormality of apoprotein E with excess of abnormal lipoprotein (beta mobility-VLDL); TC >300 mg/dL plus TG >400 mg/dL should suggest this diagnosis.
VLDL cholesterol:TG ratio = 0.3 (normal ratio = 0.2).
Diagnosis by combination of ultracentrifugation and isoelectric focusing that shows abnormal apoprotein E pattern.
Tuberous and tendinous xanthomas and palmar and plantar xanthomatous streaks are present.
Atherosclerosis is more common in peripheral than coronary arteries.
Familial Hypertriglyceridemia (Type IV)
Familial hypertriglyceridemia is an autosomal dominant condition present in 1% of general population and 5% of survivors of AMI <age 60 years.
Elevated TG (usually 200–500 mg/dL) and VLDL with normal LDL-C and decreased HDL-C.
Table 12-9. Comparison of Classic Types of Hyperlipoproteinemia
Point of Comparison Type I (Rarest) Type II-a (Relatively Common) Type II-b (Relatively Common) Type III (Relatively Uncommon) Type IV (Most Common) Type V (Uncommon)
Origin Exogenous hyperlipidemia due to deficient lipoprotein lipase   Overindulgence lipidemia   Endogenous hyperlipidemia Mixed endogenous and exogenous hyperlipidemia (combined types I and IV)
Definition Familial fat-induced hyperglyceridemia Hyperbetalipoproteinemia (hypercholesterolemia) Combined hyperlipidemia (mixed hyperlipidemia) Carbohydrate-induced hyper-glyecridemia with hypercholesterolemia
Not known younger than age 25 yrs
Carbohydrate-induced hyper-glyceridemia without hyper-cholesterolemia
Only occasionally seen in children
Combined fat- and carbohydrate-induced hypergly-ceridemia
Age Usually younger than age 10 yrs  
Gross appearance of plasma On standing: supernatant creamy, infranatant clear Clear (no cream layer on top) No cream layer on top; clear to turbid infranatant Clear, cloudy, or milky Slightly turbid to cloudy
On standing: unchanged
Markedly turbid On standing: supernatant, creamy, infranatant milky
Serum cholesterol N or slightly I Markedly I (300–600 mg/dL) Markedly I (300–600 mg/dL) Markedly I (300–600 mg/dL) N or slightly I I (250–500 mg/dL)
LDL cholesterol N I I I N N
HDL cholesterol N to D N to D N to D N to D N to D N to D
Apolipoprotein (apo) I (B-48)
I (A-IV)
V (C-II)
I (B-100) I(B-100) I(E-II)
D(E-III)
D(E-IV)
V(C-II)
I(B-100)
V(C-II)
I(B-48)
I(B-100)
Increased lipoprotein Chylomicrons LDL LDL, VLDL IDL VLDL VLDL, chylomicrons
Serum triglycerides Markedly I (usually >2,000 mg/dL) N 1 ≤ 400 mg/dL Markedly I (200–1,000 mg/dL) Markedly I (500–1,500 mg/dL) Markedly I (500–1,500 mg/dL)
Appearance of lipoprotein components visualized by electrophoresis  
    Chylomicrona Marked I 0 0 0 0  
    Beta-lipoproteinb N or D I I I, floating beta N or I I
    Pre–beta-lipoproteinc N or D N I I I  
    Alpha-lipoproteind  
Other laboratory abnormalities Glucose tolerance usually N   Hyperglycemia; glucose tolerance often abnormal; serum uric acid I Glucose tolerance often abnormal; serum uric acid often I Glucose tolerance usually abnormal; serum uric acid usually I
Triglyceridecholesterol ratio 8 1 Variable <2 1–5 >5
Lipid changes resembling primary hyperlipidemias   Very high cholesterol diet Same as for type II-a Caffeine or alcohol before testing  
    Diet
    Drugs
  Triglyceride-lowering drugs in types III and IV Same as for type II-a Triglyceride-lowering drugs in type IV Cholesterol-lowering drugs, chlorothiazide, birth control pills, or estrogens  
  aChylomicrons cVLDL IDL bLDL dHDL
Origin Gut Liver VLDL VLDL and IDL Liver, gut, intravascular metabolism
Function Transport dietary triglycerides Transport endogenous triglycerides Transport cholesteryl esters; LDL precursor Transport cholesteryl esters Reverse cholesterol transport
Electrophoretic mobility Origin Pre-beta Beta, pre-beta Beta Alpha
Major apolipoproteins B-48, A-1, C, E B-100, C, E B-100, E B-100 A-I, A-II, C, E
Protein 1% 10% 15% 20% 50%
Triglyceride 90% 60%   5% 5%
Cholesterol 5% 15% 35% 50% 20%
Phospholipid 4% 15%   25% 25%
0 = absent; D = decreased; I = increased; N = normal; HDL = high-density lipoprotein; IDL = intermediate density; LDL = low-density lipoprotein; VLDL = very low density lipoprotein.
Since apo B is the only protein in LDL and apo A-I is the major protein constituent of HDL and VLDL, the ratio of apo-B to apo A-I reflects the ratio of LDL to HDL and may be a better discriminator of coronary artery disease than the individual components; however, data on apolipoproteins are still limited. Obtain blood only after at least 12–14 hrs’ fasting and when patient has been on usual diet for at least 2 wks.
Rule out diabetes, pancreatitis, and hypothyroidism in all groups.
Increased susceptibility to coronary artery disease occurs in types II, III, and IV; accelerated peripheral vascular disease in type III.
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Distinction from familial combined hyperlipidemia is made only by extensive family screening.
Abetalipoproteinemia (Bassen-Kornzweig Syndrome)
Abetalipoproteinemia is a rare autosomal recessive disorder in which the liver and intestine cannot secrete Apo B; should be ruled out in children with fat malabsorption, steatorrhea, failure to thrive, neurologic symptoms, pigmented retinopathy, acanthocytosis.
  • Abnormal RBCs (acanthocytes) are present in the peripheral blood smear; may be 50% to 90% of RBCs and are characteristic (see Chapter 11).
Decreased RBC life span may vary from severe hemolytic anemia to mild compensated anemia.
  • Erythrocyte sedimentation rate (ESR) is markedly decreased (e.g., 1 mm/h).
  • There may be
    • Marked decrease of serum beta-lipoprotein and cholesterol.
    • Marked decrease in serum TG (<30 mg/dL) with little increase after ingestion of fat, and in TC (20–50 mg/dL).
    • Chylomicrons, LDL-C, VLDL, Apo B-48, and Apo B-100 are absent; HDL-C may be lower than in normal persons.
    • Marked impairment of GI fat absorption.
    • Low serum carotene levels.
    • Abnormal pattern of RBC phospholipids.
Plasma lipids are normal in heterozygotes.
Malabsorption causes low serum fat-soluble vitamin (A, K, E) levels.
  • Biopsy of small intestine shows characteristic lipid vacuolization, but this is not pathognomonic (occasionally seen in celiac disease, tropical sprue, juvenile nutritional megaloblastic anemia).
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Negative sweat test distinguishes this from cystic fibrosis.
Arteriosclerosis is absent.
A variant is normotriglyceridemic abetalipoproteinemia in which patient can secrete Apo B-48 but not Apo B-100, resulting in normal postprandial TG values but marked hypocholesterolemia; associated with mental retardation and vitamin E deficiency.
Hypobetalipoproteinemia
Hypobetalipoproteinemia is an autosomal dominant disorder with increased longevity and lower incidence of atherosclerosis; at least one parent will show decreased β-lipoprotein.
Marked decrease in LDL-C and LDL-C/HDL-C ratio.
Homozygous patients have decreased serum TC (<50 mg/dL) and TG and undetectable or trace amounts of chylomicrons, VLDL, and LDL.
Heterozygotes are asymptomatic and have serum TC, LDL-C, and Apo B values that are 50% of normal (consistent with codominant disorder). May also be caused by malabsorption of fats, infection, anemia, hepatic necrosis, hyperthyroidism, AMI, acute trauma.
Tangier Disease
Tangier disease is a rare autosomal recessive disorder caused by mutations at chromosome 9q31 causing a defect in the metabolism of Apo A, in which there is a marked decrease (heterozygous) or absence (homozygous) of HDL.
  • Plasma levels of Apo A-I and A-II are extremely low. In homozygotes, HDL-C is usually <10 mg/dL and Apo A-I is usually <5 mg/dL. In heterozygotes, HDL-C and Apo A-I are ∼50% of normal.
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Pre-beta lipoprotein is absent.
Serum TC (<100 mg/dL), LDL-C, and phospholipids are decreased; TG = 100 to 250 mg/dL.
Deposits of cholesterol esters in reticuloendothelial cells cause enlarged liver, spleen, and lymph nodes; enlarged orange tonsils; and small orange-brown spots in rectal mucosa. Patients may have premature CAD, mild corneal opacification, and neuropathy in homozygous type.
Lecithin-Cholesterol Acyltransferase Deficiency (Familial)
Lecithin-cholesterol acyltransferase (LCAT) deficiency is a very rare autosomal recessive disorder of adults. It is associated with premature CAD, corneal opacities, glomerulosclerosis.
Serum TC is normal but cholesterol esters are virtually absent. Plasma free cholesterol is extremely increased. HDL-Cs low.
Normochromic anemia with large RBCs that are frequently target cells.
Proteinuria.
Isolated Lipidemias
High HDL-C
High HDL-C is a rare autosomal recessive disorder causing cholesteryl ester transfer protein gene defects.
Due To
Active life style (physical exercise)
Drugs (e.g., estrogens, alcohol, phenytoin, phenobarbital, rifampicin, griseofulvin)
Low HDL-C
Due To
Sedentary life style (physical inactivity)
Drugs (isotretinoin, anabolic steroids)
Familial hypoalphalipoproteinemia (autosomal dominant disorder with HDL-C)
Deficiency of Apo A-I and Apo C-III
Abetalipoproteinemia, hypobetalipoproteinemia (<30 mg/dL in women and <40 mg/dL in men)
Hyperlipidemias, Secondary
Due To
(Many are combined hyperlipidemias)
  • Diabetes mellitus*
    Increased VLDL with increased serum TG, low HDL-C; LDL-C may be normal or mildly increased.
  • Hypothyroidism
    Increased LDL-C and TC. Test for hypothyroidism whenever LDL-C>190 mg/dL.
    Rapidly becomes normal with treatment.
    Serum TC is not always increased.
  • Nephrotic syndrome*
    Increased serum TC and LDL-C is usual.
    Increased VLDL and therefore increased serum TG may also occur.
  • Other renal disorders (chronic uremia, hemodialysis, following transplantation)
    Increased TG and TC and low HDL-C may occur.
  • Hepatic glycogenoses
    Increased serum lipoprotein is common in any of the forms, but the pattern cannot be used to differentiate the type of GSD.
    Predominant increase in VLDL in G6PD deficiency.
    Predominant increase in LDL-C in debrancher and phosphorylase deficiencies.
  • Obstructive liver disease*
    Increased serum TC is common until liver failure develops.
    Resistant to conventional drug therapy. The type of lipoproteinemia is variable.
    Fig. 12-5. Algorithm for neonatal hyperammonemia.
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    In intrahepatic biliary atresia, there is often an increase in lipoprotein X, with a marked increase in serum TC and even more marked increase in serum phospholipids.
  • Chronic alcoholism
    Marked increase in VLDL, producing type IV or V patterns.
    • Hyperlipoproteinemia of “affluence” (dietary)*
    • Pregnancy*
    • Drugs (e.g., estrogens*, steroids*, beta blockers*, diuretics, cyclosporine)
Disorders of Amino Acid Metabolism
Genetic disorders of amino acid metabolism may be caused by:
  • Enzyme defects
  • Membrane transport defects
  • Miscellaneous (including storage diseases)
Enzyme deficiency may be caused by:
  • Defective synthesis rate
  • Synthesis of abnormal protein
  • Multiple abnormal alleles may affect the same enzyme protein
Clinical findings depend on:
  • Location of block (deficiency distal to block or toxic increase proximal to block)
  • Degree of abnormality
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  • Interrelationships of various pathways
  • Production of abnormal metabolites
Alkaptonuria
Alkaptonuria is an extremely rare autosomal recessive deficiency of liver homogentisic oxydase (gene located on chromosome 3q21-q231), causing accumulation of homogentisic acid, ochronosis, and destruction of connective tissue. Cardinal features of the disease are urine changes, pigmentation of sclera and ear cartilage, and lumbosacral spondylitis (ochronosis). It may also cause deformity of aortic valve cusps.
  • Presumptive diagnosis by urine that becomes brown-black on standing and reduces Benedict solution (urine turns brown) and Fehling solution, but glucose-oxidase reagent strips are negative. Ferric chloride test is positive (urine turns purple-black).
  • Thin-layer chromatography and spectrophotometric assay identify marked increase in urinary homogentisic acid (is normally undetectable) but are not generally necessary for diagnosis.
  • An oral dose of homogentisic acid is largely recovered in the urine of affected patients but not in normal persons.
Kidney stones occur with increased frequency.
Urine may contain increased osteocalcin (due to new bone formation) and collagen N-telopeptide (because of bone resorption).
Aminoaciduria, Secondary
Occurs in
  • Severe liver disease
  • Renal tubular damage caused by:
    Lysol
    Heavy metals
    Maleic acid
    Burns
    Galactosemia
    Wilson disease
    Scurvy
    Rickets
    Fanconi syndrome (e.g., outdated tetracycline, multiple myeloma, inherited)
  • Neoplasms:
    Cystathionine excretion in neuroblastoma of adrenal gland
    Ethanolamine excretion in primary hepatoma
Argininosuccinic Aciduria
Argininosuccinic aciduria is an autosomal recessive deficiency of argininosuccinase that may cause brittle hair, neurologic changes, and absence of metabolic acidosis. More than 12 mutations are located on chromosome 7cen-q11.2.
  • Fasting blood ammonia is normal but may be markedly increased after eating.
  • Argininosuccinic acid is markedly increased in plasma and urine; it may also be increased in cerebrospinal fluid (CSF).
Because of block in urea cycle, plasma arginine is markedly decreased, and glutamine and alanine are increased.
Urine orotic acid is increased.
Serum ALP may be increased.
  • Heterozygous carriers show increased argininosuccinic acid in urine and decreased argininosuccinase in RBCs, liver biopsy, and cultured skin fibroblasts.
  • Prenatal diagnosis by assay of enzyme in cultured amniocytes (Mycoplasma contamination may cause a false-negative result) or assay of amniotic fluid for argininosuccinic acid.
Neonatal type is usually fatal in infancy. Late-onset type may present at any age triggered by intercurrent infection or stress.
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Table 12-10. Summary of Primary Overflow Aminoacidurias (Increased Blood Concentration with Overflow into Urine)
Disease Increased Blood Amino Acids Urine Abnormalities* Other Laboratory Findings
Phenylketonuria Phenylalanine Orthohydroxyphenylacetic acid; phenylpyruvic, acetic, and lactic acids Blood tyrosine does not rise after phenylalanine load
Maple syrup urine disease  
    Severe infantile form Valine, leucine, isoleucine, alloisoleucine Branched-chain ketoacids in great excess: urine has odor of maple syrup  
    Intermittent form Same Ketoaciduria and urine odor present only during attacks  
Hypervalinemia Valine  
Homocystinuria Methionine; homocystine Homocystine in great excess in urine Vascular accidents, Marfan-like syndrome, osteoporosis
Tryptophanemia Tryptophan Decreased excretion of kynurenine after tryptophan load  
Hyperlysinemia Lysine Ornithine, gamma-aminobutyric acid, and ethanolamine in excess  
Congenital lysine intolerance Lysine, arginine   Ammonia intoxication
Tyrosinosis Tyrosine; methionine may be markedly increased p-Hydroxyphenylpyruvic, acetic, and lactic acids; methionine may be prominent Generalized aminoaciduria, renal glycosuria, renal rickets, cirrhosis, Fanconi’s syndrome
Cystathioninuria Cystathionine slightly increased Cystathionine (may be >1 gm/day) Congenital acidosis, thrombo-cytopenia, pituitary gland abnormalities
Hyperglycinemia  
  Severe infantile Glycine (other amino acids may be elevated) Acetone May have ammonia intoxication, ketosis, neutropenia, and osteoporosis
  With hypo-oxalusia Glycine Decreased oxalate excretion  
Argininosuccinicaciduria Argininosuccinic acid (∼4 mg/dL); Citrulline Argininosuccinic acid (2.5–9.0 gm/day); Citrulline Ammonia intoxication
Citrullinemia Citrulline; alanine Citrulline; glutamine Liver disease, ammonia intoxication; BUN may be low
Ornithinemia Ornithine Ornithine may be normal Ammonia intoxication
Histidinemia Histidine (alanine may also be increased) Alanine may be increased; imidazolepyruvic, acetic, and lactic acids Urocanic acid absent in sweat and urine after oral histidine load
Carnosinuria   Carnosine (20–100 mg/day)  
Hyper-beta-alaninemia Beta-alanine, GABA Beta-aminoisobutyric acid, GABA, and taurine in excess Beta-alanine and GABA increased in CSF
Hyperprolinemia  
  Type I Proline Hydroxyproline, glycine elevated Patient may have hereditary nephritis
  Type II Proline Delta1-pyrroline 5-carboxylate, hydroxyproline, glycine elevated No nephritis
Hydroxyprolinemia Hydroxyproline No excretion of delta1-pyrroline 3-hydroxy-5-carboxylate or gamma-hydroxyglutamic acid after hydroxyproline load  
Hypophosphatasia Phosphoethanolamine slightly elevated (∼0.4 mg/dL) Phosphoethanolamine (≥ 150 mg/day) Bone disease
GABA = gamma-aminobutyric acid.
*In addition to overflow aminoaciduria:
Mental retardation is often present in these patients.
For proper interpretation of aminoaciduria, avoid all drugs and medications for 3–4 days (unless immediate diagnosis is required), since they may cause renal tubular damage with aminoaciduria or may produce confusing spots on chromatograms. Use fresh urine specimens without urinary tract infection or else amino acid pattern may be abnormal. Since aminoaciduria may occur with various acute illnesses, repeat amino acid chromatogram after recovery from acute illness to avoid misdiagnosis. Some aminoacidurias may not be clinically significant (e.g., newborn aminoaciduria, glycinuria, beta-aminoisobutyricaciduria).
Source: Efron MD, Ampola MG. The aminoacidurias Pediatr Clin North Am 1967;14:881.
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Table 12-11. Summary of Renal or Gut Transport Aminoacidurias (Blood Amino Acids Are Normal or Low)
Disease Amino Acids Increased in Urine
Oasthouse urine disease Methionine (may not be much increased on normal diet but is on high-methionine diet); smaller amounts of valine, leucine, isoleucine, tryosine, and phenylalanine
Hartnup disease Neutral amino acids (monoamine, monocarboxylic acid) and basic amino acids (methionine, proline, hydroxyproline, and glycine) normal or only slightly increased
Glycinuria (may be harmless; patient may be heterozygous for benign prolinuria; may be associated with many conditions) Glycine
Severe prolinuria (Joseph’s syndrome) Proline, hydroxyproline, and glycine in great excess (≤3 gm/day of proline)
Benign prolinuria Proline, hydroxyproline, and glycine (≤600 mg/day of proline)
Cystine-lysinuria Cystine and dibasic amino acids
  Type I (renal calculi)
  Type II
  Type III
Isolated cystinuria (familial hypoparathyroidism, ? incidental) Cystine
Source: Efron MD, Ampola MG. The aminoacidurias. Pediatr Clin North Am 1967;14:881.
Beta-Aminoisobutyricaciduria
Beta-aminoisobutyricaciduria is a familial disorder of thymine metabolism. It is a benign metabolic polymorphic trait.
  • Increased beta-aminoisobutyric acid in urine (50–200 mg/24 h)
May also occur in leukemia because of increased breakdown of nucleic acids.
Carnitine Deficiency
Carnitine deficiency is a very rare autosomal recessive disorder of mitochondrial fatty acid metabolism caused by impaired carnitine transport in muscle, heart, fibroblasts, and renal and intestinal epithelia.
Two types
  • Myopathic: Deficiency limited to muscle; normal levels in plasma and other tissues. Myoglobinuria in older children or young adults. Biopsy shows lipid deposits. Tissue homogenates do not support normal rates of beta-oxidation of long-chain fatty acids unless carnitine is added. Serum carnitine is normal or slightly decreased.
  • Systemic: More acute clinical picture, presents earlier in life; may mimic Reye syndrome.
Carnitine depleted in blood and all tissues.
Tissue contains marked decreased activity of medium-chain acyl coenzyme A (CoA) dehydrogenase.
Hepatic encephalopathy
Hypoglycemia without ketosis
Hyperammonemia may be present
Increased serum uric acid may be present
Laboratory findings due to cardiomyopathy
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Due To
  • Dietary deficiency
  • Low renal reabsorption (e.g., Fanconi syndrome)
  • Inborn deficiency of medium-chain acyl CoA dehydrogenase
  • Valproic acid therapy (inducing excretion of valprolycarnitine in urine)
  • Excessive loss of free carnitine in urine because of failure of carnitine transport across cells of renal tubule, muscle, and fibroblasts
  • Organic acidurias (e.g., methylmalonic aciduria, propionic acidemia)
  • Others (e.g., maternal deficiency, prematurity)
Citrullinemia
Citrullinemia is a rare autosomal recessive deficiency of argininosuccinate synthetase with metabolic block in citrulline utilization and associated mental retardation. It is genetically heterogeneous (like other disorders of the urea cycle), with various clinical pictures and onset from neonatal to adult period. Many mutations are identified, located at chromosome 9q34.
  • Massive hyperammonemia (>1,000 mg/dL) in neonatal form.
  • Markedly increased citrulline levels in blood, CSF, and urine in acute neonatal citrullinemia. May also be mildly to moderately increased in argininosuccinic aciduria.
  • Blood argininosuccinic acid is absent.
  • Serum levels of glutamine and alanine are usually increased.
  • Urine orotic acid is increased.
Laboratory findings due to liver disease.
  • Deficient enzyme activity can be demonstrated in liver biopsy and cultured skin fibroblasts.
  • Prenatal diagnosis by assay of citrulline in amniotic fluid or of enzyme in cultured amniocytes. Carrier detection is available.
Cystathioninuria
Cystathioninuria is a rare autosomal recessive deficiency of cystathionine γ-lyase, probably a benign trait, that is corrected by vitamin B6.
Increased cystathionine in urine
Glutaric Acidemia (Type I)10
Glutaric acidemia is an autosomal recessive inborn error of metabolism caused by a deficiency of glutaryl-CoA dehydrogenase, resulting in progressive neurodegenerative disease. Glutaryl-CoA dehydrogenase is a mitochondrial matrix enzyme encoded by nuclear gene on chromosome 19p13.2.
  • Deficiency of this enzyme causes accumulation of glutaric acid and its metabolites (glutaconic acid and 3-hydroxyglutaric acid) which can be detected in urine by gas chromatographic (GC) MS and is diagnostic.
  • Deficiency of this enzyme occurs in cultured skin fibroblasts.
  • Prenatal diagnosis and carrier detection are available
  • Can also use dried blood spots for newborn screening (increased glutarylcarnitine) by MS/MS. May be negative in asymptomatic persons.
Footnote
10
Rakheja D, et al. Lab Med 2005;36:174.
Histidinemia
Histidinemia is a rare autosomal recessive deficiency of histidase in liver and skin (converts histidine to urocanic acid). It results from mutations at 12q22-q23.
  • Plasma histidine is increased to 500 to 1,000 μmol/L (normal = 85–120 μmol/L).
  • Urine histidine is increased to 0.5 to 4.0 g/d (normal <0.5 g/d). Histidine metabolites (imidazole acetic, imidazole lactic, and imidazole pyruvic acids) are also increased in urine; alanine may be increased.
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Urine may show green color with Phenistix or ferric chloride test because of imidazole pyruvic acid.
With oral histidine load, no FIGLU appears in urine.
Most children show no sequelae; therefore neonatal screening is not performed.
Heterozygote detection is not established yet.
Homocystinuria/Homocysteinemia
Homocystinuria/homocystinemia are caused by a genetic deficiency of methionine synthase on chromosome 1q43. Homocysteine is the reduced (sulfhydryl) form and homocystine is the oxidized (disulfide) form of homologues cysteine and cystine. The term refers to the combined pool of homocystine and homocysteine and their mixed disulfides. May also be caused by inherited disorders in folate or cobalamin metabolism.
Use
Unexplained thromboembolic disease. Homocystinemia is independent risk factor for premature arteriosclerosis (e.g., coronary, cerebral, and peripheral vessels) and venous thromboembolic disease. Gradient response to risk of thrombosis: <7.0 μmol/L = no risk; 9.0 μmol/L = low risk; 14.0 μmol/L = moderate risk; >14.0 μmol/L = high risk.
Early diagnosis of cobalamin deficiency.
Due To
Autosomal recessive error of methionine metabolism with deficient methionine synthase in liver and brain, with inability to catalyze homocysteine to methionine. Incidence of mild form = 5% to 7% of general population; severe form is rare.
May also be caused by other rare genetic disorders, e.g., cobalamin C disease.
Increased In
Deranged vitamin B12 metabolism, block in folate metabolism, or deficiency of vitamin B12, folate, or vitamin B6
Chronic renal or liver failure, postmenopausal state, drugs (e.g., methotrexate, phenytoin, theophylline, cigarette smoking)
Various neoplastic diseases (e.g., acute lymphoblastic leukemia, cancers of breast, ovary, pancreas)
Preanalytic factors, e.g., nonfasting sample, delay in separating plasma from cells
  • Urine excretion of homocysteine is increased (positive nitroprusside screening test). May also contain increased methionine and other amino acids.
  • Increased serum homocysteine (up to 250 mg/d; normal = trace or not detected) and methionine (up to 2,000 mg/d; normal up to 30 mg/d); also increased in CSF.
  • Abnormal homocysteine metabolism may only be shown after methionine-loading test. Blood samples before and at 4- to 8-hour intervals after 100 mg/kg methionine oral load. Normal = transient increase free and protein-bound homocysteine peaking between 4 and 8 hours. Abnormal = plasma homocysteine >2 SD greater than normal controls.
In homozygous form, laboratory findings due to associated clinical conditions:
  • Mild variable hepatocellular dysfunction
  • Mental retardation, Marfan syndrome, osteoporosis, etc.
Serum methionine levels should be kept at 20 to 150 μmol/L by a low-methionine diet and pyridoxine therapy.
  • Patients have enzyme activity levels of 0% to 10% in fibroblasts and lymphocytes; heterozygotes (their parents) have levels <50% of normal.
  • For neonatal detection, measure methionine in filter paper specimen of blood; confirm by measuring blood and urine amino acids. Methionine tends to be very low in newborns.
  • Can also measure specific enzyme in cultured fibroblasts.
Hydroxyprolinemia
Hydroxyprolinemia is a very rare autosomal recessive benign trait.
  • Increased hydroxyproline in blood
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Hyperglycinemia
Hyperglycinemia is a rare autosomal recessive disease with ketotic and long-chain ketotic forms (without hypoglycemia) and ketonuria accentuated by leucine ingestion.
Same findings (neutropenia, thrombocytopenia, hypogammaglobulinemia, increased glycine in blood and urine, osteoporosis, hypoglycemia) may occur in propionic acidemia, methylmalonic acidemia, isovaleric acidemia, and 3-keto-thiolase deficiency.
Hyperoxaluria
Hyperoxaluria is a rare autosomal recessive organic acid disorder.
Type I (glycolic aciduria) is caused by deficiency of alanine:glyoxylate aminotransferase (converts glycolic acid to glycine). In absence, glycolic acid is converted to oxalic acid.
  • Early childhood calcium oxalate renal calculi and nephrocalcinosis with extrarenal deposition of calcium oxalate in eye, heart, skin, other sites. Uremia causes death.
  • Increased glycolic and oxalic acid in urine in large amounts.
Type II (glyceric aciduria), caused by deficiency of glyceric dehydrogenase or glycerol kinase, is milder and may be asymptomatic.
  • Increased serum and urinary oxalic acid
Increased urinary glycolic and glyoxylic acid
Must be distinguished from secondary increased absorption from bowel (e.g., inflammatory bowel disease, fat malabsorption)
Hyperprolinemia
There are two types of hyperprolinemia, caused by rare autosomal recessive traits. Type I is benign and due to decreased activity of proline oxidase encoded on chromosome 22q11.2. Type II may have seizures; due to deficient activity of delta-1-pyrroline-5-carboxylate-dehydrogenase encoded on chromosome 1p36.)
Type II shows
  • Increased proline in blood and urine
Increased glycine and hydroxyproline in urine
Severe prolinuria (Joseph syndrome)
  • Urine shows marked increase in proline, hydroxyproline, and glycine.
Heterozygotes may show mild prolinuria.
Type II shows same findings as Type I, along with:
  • Increased blood and urine levels of pyrroline-5-carboxylate and increased urine level of pyrroline-3-hydroxy-5 carboxylate.
  • Deficient enzyme activity in WBCs and cultured skin fibroblasts.
Maple Syrup Urine Disease11
Maple syrup urine disease (MSUD) is caused by an autosomal recessive deficiency of mitochondrial multienzyme complex branched-chain α-keto acid-dehydrogenase; the incidence is about 1 in 200,000 live births. There is a characteristic maple syrup odor in urine, sweat, hair, and cerumen. Genes are encoded at chromosomes 19q13.1-q13.2, 6p22-p21, and 1p31.
  • Blood shows greatly increased branched-chain amino acids (leucine, isoleucine, and valine) and their ketoacids. Presence of alloisoleucine (stereoisomeric metabolite of isoleucine) is characteristic.
  • Metabolic ketoacidosis occurs, often with hyperammonemia and hypoglycemia.
  • Ferric chloride test of urine produces green-gray color.
  • Newborn screening testing for leucine may be available.
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  • MSUD is divided into six severity classes (Ia, Ib, II, III, IV, V) depending on which enzyme has been mutated and identifying that enzyme.
Loading tests with isoleucine and measuring increased alloisoleucine in blood may be performed for variant MSUD.12
Patient must be monitored to avoid ketoacidosis.
  • Prenatal diagnosis can be performed by measuring enzyme concentration in cells cultured from amniotic fluid.
Footnote
12
Schadewaldt P, Bodner-Leidecker A, Hammen HW, Wendel U. Significance of L-alloisoleucine in plasma for diagnosis of maple syrup urine disease. Clin Chem 1999;45:1734–1740.
Methylmalonic Acidemia
Methylmalonic acidemia is a very rare autosomal recessive error of metabolism, with neonatal metabolic acidosis and mental and somatic retardation. There are at least four distinct forms; the screening incidence is 1 in 48,000 in infants 3 to 4 weeks old.
  • Metabolic acidosis
  • Increased methylmalonic acid in urine and plasma
Long-chain ketonuria
Intermittent hyperglycinemia
  • All findings accentuated by high-protein diet or supplemental ingestion of valine or isoleucine
Hypoglycemia, neutropenia, thrombocytopenia may occur
Heterozygote detection is not reliable
  • Prenatal diagnosis by assay of methylmalonyl CoA mutase in cultured amniocytes, increased methylcitric or methylmalonic acids in amniotic fluid, or (late in pregnancy) increased methylmalonic acid in maternal urine
  • Identify by MS/MS spectrometry
Methylmalonic acidemia and aciduria are direct measures of tissue vitamin B12 deficiency. (See Chapter 11.)
Nephron Transport Defects, Classification
Proximal Tubule
Selective transport defects
(A) Renal glycosuria (primary; combined)
(B) Renal aminoaciduria
  • 1. Basic aminoacidurias
    • (a) General cystinuria (cystine, lysine, arginine, ornithine)
    • (b) Specific hypercystinuria, dibasic aminoaciduria, lysinuria
  • 2. Neutral aminoacidurias
    • (a) General (Hartnup disease)
    • (b) Specific (methioninuria, tryptophanuria, histidinuria)
  • 3. Dicarboxylic aminoaciduria
    • (a) General (glutamic, aspartic acids)
  • 4. Iminoglycinuria
    • (a) General (proline, hydroxyproline, glycine)
    • (b) Specific (glycinuria)
(C) Proximal RTA (primary or due to carbonic anhydrase change)
(D) Uric acid disorders
(E) Calcium and phosphate disorders
Nonselective (Fanconi syndrome)
  • Genetic (e.g., cystinosis, tyrosinemia, Wilson disease)
  • Tubulointerstitial (e.g., Sjögren syndrome, medullary cystic disease, renal transplant)
  • Heavy metals (lead, cadmium, mercury)
  • Drugs, toxins (e.g., outdated tetracycline, gentamicin)
  • Monoclonal gammopathies (see Chapter 11)
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  • Secondary hyperparathyroidism
  • Others (e.g., nephrotic syndrome, amyloidosis, paroxysmal nocturnal hemoglobinuria)
Loop of Henle
Bartter syndrome
Drugs (e.g., ethacrynic acid, furosemide)
Distal Tubule
I. Selective transport defects
(A) Distal RTA
  • 1. Genetic disorders (e.g., medullary cystic disease [see Chapter 14], sickle cell anemia, elliptocytosis [see Chapter 11])
  • 2. Nephrocalcinosis (e.g., hyperparathyroidism, hyperthyroidism, medullary sponge kidney, Wilson disease, Fabry disease)
  • 3. Tubulointerstitial (e.g., chronic pyelonephritis, obstructive uropathy, renal transplant) (see Chapter 14)
  • 4. Autoimmune disorders (e.g., Sjögren syndrome, SLE, primary biliary cirrhosis)
  • 5. Drugs (e.g., analgesics, amphotericin B)
(B) Renal tubular acidosis of glomerular insufficiency (see Chapter 14)
(C) Potassium secretory disorders
II. Nonselective transport defects (distal RTA, hyperkalemia, renal salt wasting) (see Chapter 13)
  • Primary mineralocorticoid deficiency
  • Hypoangiotensinemia drugs (e.g., captopril, angiotensin receptor blockers)
  • Hyporeninemic hypoaldosteronism (e.g., diabetic nephropathy, tubulointerstitial nephropathies, nephrosclerosis, AIDS, nonsteroidal anti-inflammatory drugs)
  • Mineralocorticoid-resistant hyperkalemia with or without salt wasting
Medullary Collecting Ducts (see Chapter 13)
Disorders of concentration and dilution (e.g., diabetes insipidus, syndrome of inappropriate excretion of antidiuretic hormone, others)
Oasthouse Urine Disease
Oasthouse urine disease is an autosomal recessive disorder of methionine malabsorption in GI tract with diarrhea, failure to thrive, mental retardation, and white hair.
  • Distinctive odor of urine
Increase of various amino acids in blood and also in urine (e.g., phenylalanine, tyrosine, methionine, valine, leucine, isoleucine)
Ornithine Transcarbamoylase Deficiency
This is caused by an X-linked recessive deficiency of ornithine transcarbamoylase (OTC), a mitochondrial enzyme in the urea cycle that converts ornithine to citrulline. This disorder may cause seizures, cerebral palsy, mental retardation, hyperammonemic encephalopathy, and death.
  • Increased blood ammonia, usually 2× to 10× normal; glutamine, glycine, alanine are increased.
  • Markedly decreased citrulline and decreased arginine in blood.
  • Markedly increased orotic acid in blood and urine. May also be increased in lysinuric protein intolerance.
  • Decreased OTC in biopsy of liver.
  • To detect asymptomatic carriers, female heterozygotes may require measurement of urine orotic acid before and 6 hours after an oral protein loading test. Can also be
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    detected by a cDNA probe for the ornithine transcarbamylase gene using restriction fragment length polymorphism analysis (RFLP).
    Fig. 12-6. Pathways of phenylalanine metabolism.
  • Prenatal diagnosis using RFLP for chorionic villus DNA analysis.
OTC deficiency can occur after a bacterial or viral infection, causing confusion with Reye syndrome.
Phenylketonuria
PKU is an inherited autosomal recessive disorder caused by a variety of mutations on chromosome 12. The absence of phenylalanine hydroxylase activity in liver causes increased phenylalanine and its metabolites (phenylpyruvic acid, ortho-hydroxyphenylacetic acid) in blood, urine, and CSF; tyrosine and the derivative catecholamines are deficient. The condition results in mental retardation. Among Caucasians, 1 in 50 persons is a carrier and ∼1 in 12,000 in the United States is affected with PKU. See Figure 12-6.
Unrestricted protein diet:
  • Normal blood phenylalanine = 2 mg/dL.
  • • Classic PKU patients: high blood phenylalanine (usually >30 mg/dL and always >20 mg/dL in infancy) with phenylalanine and its metabolites in urine; normal or decreased tyrosine concentration.
  • • Less severe variant forms of PKU: blood phenylalanine levels are 15 to 30 mg/dL and metabolites may appear in urine (incidence = 1:15,000).
  • • Mild persistent hyperphenylalaninemia: blood phenylalanine may be 2 to 12 mg/dL and metabolites are not found in urine (incidence 1:30,000).
  • For screening of newborns, urine amounts of phenylpyruvic acid may be insufficient for detection by colorimetric methods when blood level is <15 mg/dL. May not appear in urine until 2 to 3 weeks of age. False-negative results on the Guthrie bacteria inhibition test may also occur if capillary tubes and venipuncture specimens are used for blood collection rather than direct application to filter paper, especially if level is within 0.2 mg of cutoff value. Preliminary blood screening tests detects >4 mg/dL. Screening should be performed after protein-containing feedings have begun.
  • When repeat screening test is positive, quantitative blood phenylalanine and tyrosine are performed to confirm phenylalaninemia and exclude transient tyrosinemia of newborn, which is the most common cause of a positive screening. Tandem mass spectrometry or fluorometry confirms the increased level and also measures tyrosine levels.
  • Serial determinations should be performed on untreated borderline cases, because blood levels may change markedly with time or stress and infection.
  • Diagnosis of PKU may be confirmed by giving 100 mg of ascorbic acid and collecting blood and urine 24 hours later.
Adjust diet throughout life by monitoring blood phenylalanine:
  • Up to 12 years old: 2 to 6 mg/dL.
  • After age 12: 2 to 10 mg/dL.
  • After adolescence: 2 to 15 mg/dL.
  • During pregnancy: 2 to 5 mg/dL, because with increased serum phenylalanine there is greatly increased frequency of mental retardation, microcephaly, and congenital heart disease in offspring.
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Monitoring frequency recommendations:
  • 1×/week during first year
  • 2×/month ages 1 to 12 years
  • 1×/month after age 12 years
  • 2×/week during pregnancy in women with PKU
  • Detection of heterozygotes of 75% of families and prenatal diagnosis are now possible using cDNA probe.
Laboratory findings due to congenital heart disease in ≤15% of PKU patients.
Urine FeCl3 dipstick test is positive because of phenylpyruvic acid.
Comparison of PKU and Transient Tyrosinemia
Substance PKU Transient Tyrosinemia
Serum phenylalanine >15 mg/dL >4 mg/dL (15–20 mg/dL)
Serum tyrosine <5 mg/dL (is never increased) >4 mg/dL (5–20 mg/dL)
Urine o-hydroxyphenylacetic acid Present Absent
Urine Phenylalanine is >100 μg/mL Large amounts of tyrosine and its metabolites
Propionic Acidemia
Propionic acidemia is characterized by an autosomal recessive deficiency of propionyl CoA carboxylase, which prevents degradation and therefore results in intolerance of isoleucine, valine, threonine, and methionine. Incidence in the United States = ∼1:50,000 live births.
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  • Recurrent episodes (often following infections) of massive ketosis, metabolic acidosis, vomiting, and dehydration progressing to coma.
Same picture as hyperglycinemia (see previous).
  • Increase plasma and urine glycine.
Urine is tested (daily in infants) for ketones (e.g., Acetest reagent strips or tablets) and blood for propionic acid to monitor treatment.
Laboratory findings of complications (e.g., sepsis, ventricular hemorrhage)
  • Prenatal diagnosis is available.
  • Positive assay of enzyme in cultured fibroblasts can indicate heterozygosity, but negative assay may not be reliable to indicate absence.
Renal Amino Acid Transport Disorders
Cystinuria
Cystinuria is an autosomal recessive failure of amino acid transport, resulting in renal tubular reabsorption and intestinal uptake of cystine, ornithine, lysine, arginine.
  • Markedly increased cystine in urine (20 × -30× normal). May also be increased in organic acidemias, hyperuricemia, trisomy 21, hereditary pancreatitis, muscular dystrophy, hemophilia, retinitis pigmentosa.
  • Presence of characteristic hexagonal crystals in urine is diagnostic.
  • Confirm diagnosis by identifying increased urinary arginine, lysine, and ornithine in urine. Homozygotes excrete >800 mg/24 h of cystine.
  • Cystine renal and bladder stones make up ≤8% of stones in children, 1% in adults.
Laboratory findings due to genitourinary (GU) tract infections. Bacteria can degrade cystine.
Hartnup Disease
Hartnup disease is a rare autosomal recessive defect in transport in GI tract and renal tubules of “neutral” amino acids, which causes nicotinamide deficiency (due to faulty metabolism of tryptophan) and may lead to pellagra. Incidence = 1:26,000 births.
  • Urine contains increased (5 × -1×) amounts of alanine, threonine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptamine, histidine.
Iminoglycinuria
Iminoglycinuria is a rare benign inherited autosomal recessive defect of renal tubule amino acid transport.
  • Increased urine glycine, imino acids (proline, hydroxyproline) but normal or low in blood.
Tyrosinemia
Occurs as both persistent hereditary and transient forms.
Tyrosinemia I (Hepatorenal) (Tyrosinosis) Persistent Hereditary Form
Type I tyrosinemia is a rare autosomal recessive condition caused by deficiency of fumaryl acetoacetase, with an incidence of 1 per 50,000 live births; it is usually fatal in the first year.
  • Increased blood and urine tyrosine; methionine may also be markedly increased; increased blood phenylalanine may cause positive test when screening for PKU.
  • Urinary excretion of tyrosine metabolites p-hydroxyphenylpyruvic and p-hydroxyphenylacetic acids is increased. May also be increased in myasthenia gravis, liver disease, ascorbic acid deficiency, and malignancies.
  • Detection of succinylacetone in urine is virtually diagnostic.
Acetic and lactic acids may be increased in urine.
Anemia, thrombocytopenia, and leukopenia are common.
Urine δ-aminolevulinic acid (δ-ALA) may be increased.
Laboratory findings due to Fanconi syndrome, hepatic cirrhosis, and liver carcinoma are noted.
Dietary restriction of tyrosine, phenylalanine, and methionine can correct biochemical and renal abnormalities but does not reverse or prevent progression of liver disease. A liver transplant can correct biochemical abnormalities.
  • Prenatal diagnosis by measurement of succinylacetone in amniotic fluid has been used.
Tyrosinemia II (Oculocutaneous)
Type II tyrosinemia is a rare condition caused by a deficiency of tyrosine aminotransferase.
  • Plasma tyrosine markedly increased (30–50 mg/dL)
Tyrosine is found in urine
No findings of liver or kidney disease
Tyrosinemia III
Type III tyrosinemia is caused by a deficiency of 4-hydroxyphenylpyruvic acid oxidase.
Transient Tyrosinemia
Transient tyrosinemia may occur in incomplete development of tyrosine oxidizing system, especially in premature or low-birth-weight infants.
  • Serum phenylalanine is >4 mg/dL (5–20 mg/dL).
  • Serum tyrosine is between 10 and 75 mg/dL.
  • Tyrosine metabolites in urine are ≤1 mg/mL (parahydroxyphenyl-lactic and parahydroxyphenylacetic acids can be distinguished from o-hydroxyphenylacetic acid by paper chromatography).
  • O-hydroxyphenylacetic acid is absent from urine.
Without administration of ascorbic acid, 25% of premature infants may have increased serum phenylalanine and tyrosine for several weeks (but reversed in 24 hours after ascorbic acid administration) and increased urine tyrosine and tyrosine derivatives.
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Similar blood and urine findings that are not reversed by administration of ascorbic acid may occur in untreated galactosemia, tyrosinemia, congenital cirrhosis, and giant-cell hepatitis; jaundice occurs frequently.
Serum serotonin (5-hydroxytryptophan) is decreased.
Urine 5′-hydroxyindoleacetic acid excretion is decreased.
Blood levels of phenylalanine deficiency should be monitored frequently during treatment (e.g., 2×/week during first 6 months, 1×/week during next 6 months, 2×/month up to age 18 months, 1×/month thereafter).
Adjust diet by monitoring blood phenylalanine (e.g., 10 mg/dL with consistently negative FeCl3urine test.)
In women with untreated PKU and increased serum phenylalanine, there is a greatly increased frequency of mental retardation, microcephaly, and congenital heart disease in offspring.
  • Detection of heterozygotes in 75% of families and prenatal diagnosis are now possible using cDNA probe.
Xanthinuria
Xanthinuria is a rare autosomal recessive deficiency of xanthine oxidase in tissues, which catalyzes conversion of hypoxanthine to xanthine and xanthine to uric acid.
  • Enzyme activity <10% of normal in biopsy of liver and jejunal mucosa.
  • Decreased serum uric acid; <1 mg/dL strongly suggests this diagnosis.
Decreased urine uric acid (usually <30 mg/24 h; normal up to 500 mg/24 h).
Increased urine and serum levels of xanthine and hypoxanthine.
  • Laboratory findings due to urinary xanthine calculi.
Disorders of Carbohydrate Metabolism
Fructosuria, Essential
Fructosuria is a benign asymptomatic autosomal recessive disorder caused by a deficiency of hepatic fructokinase, which metabolizes fructose to fructose-1-phosphate. The gene is encoded at chromosome 2p23.3-p23.2.
  • Large amount of fructose in urine gives a positive test for reducing substances (Benedict reagent, Clinitest) but not with glucose-oxidase methods (Clinistix, Tes-Tape).
  • Fructose is identified by paper chromatography.
  • Fructose tolerance test shows that blood fructose increases to 4× more than in normal persons, blood glucose increases only slightly, and serum phosphorus does not change.
Fructose Intolerance, Hereditary
Hereditary fructose intolerance is a severe autosomal recessive disease of infancy caused by a virtual absence of fructose-1-phosphate aldolase, causing fructose-1-phosphate accumulation in liver; clinically, it resembles galactosemia.
  • Fructose in urine of 100 to 300 mg/dL gives a positive test for reducing substances (Benedict reagent, Clinitest) but not with glucose oxidase methods (Clinistix, Tes-Tape).
  • Fructose is identified by chromatography.
  • Fructose tolerance test shows prolonged elevation of blood fructose and marked decrease in serum glucose, which may cause convulsions and coma. Serum phosphorus shows rapid prolonged decrease. Aminoaciduria and proteinuria may occur during test.
  • Fructosemia, fructosuria, hypoglycemia, and lactic acidosis are present, with increased blood potassium, magnesium, and uric acid and decreased phosphate.
Increased serum ALT, AST, and bilirubin; cirrhosis may occur.
  • Carriers and prenatal testing by molecular genetic techniques.
  • Aldolase B assay in liver biopsy confirms diagnosis.
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Fructose-1,6-Diphosphatase Deficiency
Fructose-1,6-diphosphatase deficiency is a rare severe autosomal recessive disease of infancy due to deficiency of enzyme in liver, kidney, and jejunum. It is caused by a mutation at chromosome 9q22.2-q22.3.
Episodes of hypoglycemia, lactic acidosis, increased pyruvate, alanine, uric acid, usually without fructosuria.
  • Deficient fructose-1,6-diphosphatase in WBCs and liver and jejunal biopsies.
  • Prenatal diagnosis and carrier testing are available.
Galactosemia, Classic
Classic galactosemia is an autosomal recessive inherited defect in liver and RBCs of galactose-1-phosphate uridyltransferase, which converts galactose to glucose; the deficiency causes accumulation of galactose-1-phosphate located on chromosome 9p13. Rarer variant forms are caused by galactokinase deficiency and uridinediphosphate-galactose-4-epimerase deficiency.)
  • Increased blood galactose ≤300 mg/dL (normal <5 mg/dL).
  • Increased urine galactose of 500 to 2,000 mg/dL (normal <5 mg/dL). Positive urine reaction with Clinitest but negative with Clinistix and Tes-Tape may be useful for pediatric screening up to 1 year of age.
  • Reduced RBC galactose-1-phosphate uridyltransferase establishes diagnosis.
Serum glucose may appear to be elevated in fasting state but falls as galactose increases; hypoglycemia is usual.
Galactose tolerance test is positive but not necessary for diagnosis and may be hazardous because of induced hypoglycemia and hypokalemia.
  • Use an oral dose of 35 g of galactose/m2 body area.
  • Normal: Serum galactose increases to 30 to 50 mg/dL and returns to normal within 3 hours.
  • Galactosemia: Serum increase is greater, and return to baseline level is delayed.
  • Heterozygous carrier: Response is intermediate.
  • The test is not specific or sensitive enough for genetic studies.
Albuminuria
General aminoaciduria is identified by chromatography.
Laboratory findings due to complications:
  • Jaundice (onset at age 4–10 days)
  • Liver biopsy—dilated canaliculus filled with bile pigment with surrounding rosette of liver cells, leading to cirrhosis
  • Severe hemolysis
  • Coagulation abnormalities
  • Vomiting, diarrhea, failure to thrive
  • Hyperchloremic metabolic acidosis
  • Cataracts
  • Mental and physical retardation
  • Decreased immunity (∼25% of infants develop Gram-negative [especially Escherichia coli] sepsis, which may cause death). Newborns with positive screening should be worked up for sepsis.
Findings disappear (but are not reversed) when galactose is eliminated from diet (e.g., milk). Efficacy of diet is monitored by RBC level of galactose-1-phosphate (desired range <4 mg/dL or <180 μg/g Hb).
Screening incidence = 1:7,500 live births. Cord blood is preferred, but this prevents simultaneous screening for PKU, which is normal in neonatal cord blood. Filter paper blood may show false-positive test for PKU, tyrosinemia, and homocystinuria. Test is invalidated by exchange transfusion. One in 40 persons is a carrier.
  • Prenatal diagnosis is done by measurement of galactose-1-phosphate uridyltransferase in cell culture from amniotic fluid. Parents show <50% enzyme activity in RBCs.
In galactokinase deficiency (gene located on chromosome 17q21-q25), the accumulation of galactose is reduced by alternate pathway to galactitol, causing osmotic damage to lens fibers (cataracts in childhood).
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  • • RBCs show absent galactokinase and presence of galactose-1-phosphate uridyltransferase.
  • No liver, kidney, or CNS sequelae.
Lactase Deficiency; Intestinal Deficiency of Sugar-Splitting Enzymes (Milk Allergy; Milk Intolerance; Congenital Familial Lactose Intolerance; Disaccharidase Deficiency)
Lactase deficiency is a familial disease with failure of lactose to be hydrolyzed to glucose and galactose that often begins in infancy with diarrhea, malabsorption, etc. Patients become asymptomatic when lactose is removed from the diet.
Oral lactose tolerance test shows a rise in blood sugar <20 mg/dL in blood drawn at 15, 30, 60, and 90 minutes (usual dose = 50 g). In diabetics, blood sugar may increase>20 mg/dL despite impaired lactose absorption. Test may also be influenced by impaired gastric emptying or small bowel transit.
If test is positive, repeat using glucose and galactose (usually 25 g each) instead of lactose; subnormal rise indicates a mucosal absorptive defect; normal increase (>25 g/dL) indicates lactase deficiency only.
  • Biopsy of small intestine mucosa shows low level of lactase in homogenized tissue. Is used to assess other diagnostic tests but is seldom required, except to exclude secondary lactase deficiency with histologic studies.
  • Hydrogen breath test (measured by gas chromatography) is noninvasive, rapid, simple, sensitive, and quantitative. Patient expires into a breath-collecting apparatus; complete absorption causes no increase of H2 formed in colon to be excreted in breath. Malabsorption causes H2 production by fermentation in colon that is proportional to the amount of test dose not absorbed. False-negative test in ∼20% of patients due to absence of H2-producing bacteria in colon or prior antibiotic therapy.
  • Lactose in urine amounts to 100 to 2,000 mg/dL. It produces a positive test for reducing sugars (Benedict reagent, Clinitest) but a negative test with glucose-oxidase methods (Tes-Tape, Clinistix).
After ingestion of milk or 50 to 100 g of lactose, stools have a pH of 4.5 to 6.0 (normal pH is >7.0) and are sour and frothy. Fecal studies are of limited value in adults.
Pentosuria
Pentosuria is a benign autosomal recessive deficiency in L-xylitol dehydrogenase, which catalyzes the reduction of L-xylulose to xylitol in the metabolism of glucuronic acid.
  • Urinary excretion of L-xylulose is increased (1–4 g/d), and the increase is accentuated by administration of glucuronic acid and glucuronigenic drugs (e.g., aminopyrine, antipyrine, menthol).
  • Urine positive for reducing substances but negative for glucose using glucose-oxidase enzymatic strips.
  • Heterozygotes can be detected by glucuronic acid loading, followed by measuring serum xylulose or assay nicotinamide adenine dinucleotide phosphate–L-xylulose dehydrogenase in RBCs.
Differential Diagnosis
Alimentary pentosuria—arabinose or xylose excreted after ingestion of large amount of certain fruits (e.g., plums, cherries, grapes)
Healthy normal persons—small amounts of d-ribose or trace amounts of ribulose in urine
Muscular dystrophy—small amounts of d-ribose in urine (some patients)
Sucrosuria
Sucrosuria is caused by a deficiency of sucrase.
Urine specific gravity is very high (≤1.07).
Urine tests for reducing substances are negative.
Sucrosuria may follow intravenous administration of sucrose or the factitious addition of cane sugar to urine.
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Glycogen Storage Diseases
GSDs are inherited autosomal recessive disorders (except for type IXb, which is X-linked) with abnormal concentrations or structure of glycogen molecule due to deficient activity of various enzymes in different organs. GSDs are characterized by an abnormally increased concentration of glycogen in the liver (>70 mg/g of liver) or muscle (>15 mg/g of muscle) or abnormal glycogen molecule structure. See Table 12-12.
Type IA GSD (Glucose-6-Phosphatase Deficiency; Von Gierke Disease)
Type IA GSD is caused by a lack of glucose-6-phosphatase (G6P) in liver, kidney, and intestine, with an incidence of 1:200,000 births. It may appear in the first days or weeks of life.
  • Blood glucose is markedly decreased.
  • After overnight fast, marked hypoglycemia, increased blood lactate, and occasionally pyruvate with severe metabolic acidosis, ketonemia, and ketonuria. (Recurrent acidosis is most common cause for hospital admission.)
Blood TGs are very high, cholesterol is moderately increased, and serum free fatty acids are increased. Results in xanthomas and lipid-laden cells in bone marrow.
Mild anemia is present.
Impaired platelet adhesiveness may cause bleeding tendency.
Increased serum uric acid may cause clinical gout, nephrocalcinosis, proteinuria.
Serum phosphorus and ALP are decreased.
Urinary nonspecific amino acids are increased, without increase in blood amino acids.
Other renal function tests are relatively normal despite kidney enlargement; Fanconi syndrome is rare.
Liver function tests (other than those related to carbohydrate metabolism) are relatively normal, but serum GGT, AST, and ALT may be slightly increased.
Glucose tolerance may be normal or diabetic type; diabetic type is more frequent in older children and adults.
  • Functional tests
    • Administer 1 mg of glucagon intravenously or intramuscularly after an 8-hour fast. Blood glucose increases 50% to 60% in 10 to 20 minutes in a healthy person. Little or no increase occurs in infants or young children with von Gierke disease; delayed response may occur in older children and adults.
    • Intravenous administration of glucose precursors (e.g., galactose or fructose) causes no rise in blood glucose in von Gierke disease (demonstrating block in gluconeogenesis), but normal rise occurs in limit dextrinosis (type III GSD).
  • Biopsy of liver shows absent or markedly decreased G6P on assay of frozen liver provides definitive diagnosis. Other enzymes (other GSDs) are present in normal amounts. Increased glycogen content (>4% by weight), but normal biochemically and structurally. Histologic findings are not diagnostic; show vacuolization of hepatic cells and abundant glycogen granules confirmed with Best stain.
  • Biopsy of jejunum shows intestinal glucose-6-phosphatase is decreased or absent.
Biopsy of muscle shows no abnormality of enzyme activity or glycogen content.
Can be cured by liver transplant.
Late complications include liver adenomas that tend to become malignant and progressive glomerulosclerosis with renal failure.
Type IB GSD
Type IB GSD shows all the clinical and biochemical features of von Gierke disease, except that liver biopsy does not show deficiency of G6P. It is caused by defective transport of G6P across microsomal membrane of liver cells and granulocytes.
  • May have maturation arrest neutropenia; varies from mild to agranulocytosis; usually constant but may be cyclic. Associated increased frequency of staphylococcal and Candida infections and Crohn disease.
Table 12-12. Comparison of Glycogen Storage Diseases
Type Gene Location Frequency (%) Deficient Enzyme Principal Organ Involved Usual Age at Onset Laboratory Findings
O 12p12.2   Glycogen synthetase No glycogen synthesis in liver First year Hypoglycemia, ketosis
I   20     Newborn or 3–4 mo  
  von
  Gierke
  disease
           
 Ia 17q21   Glucose-6-phosphatase Normal glycogen accumulates in liver, kidney   ↓↓↓↓glucose, ↑uric acid, ↑lipids, lactic acidosis, platelet dysfunction
 Ib 11q23   Microsomal transport of glucose-6-phosphatase Liver, WBCs   Similar to Ia but less severe. ↓↓↓↓WBs. Recurrent bacterial infections, Crohn disease
 Ic 11q23 Rare Deficient microsomal transport of phosphate Liver, kidney   Similar to Ia
II 12q25.2–q25.3 20 Lysosomal α-glucosidase      
  Pompe disease
 IIa       ↔Heart, MM Infancy Normal glycogen in lysosomes of all organs
 IIb       Heart, MM Juvenile Normal glycogen in lysosomes of MM
 IIc       MM Adult Little/no glycogen
IIIa to IIIf 1p21 20 Amylo-1,6-glucosidase (debrancher enzyme) Accumulation of highly branched, short-chain abnormal glycogen in liver. In some subtypes, also in MM and heart Infancy ↓↓Glucose
  Forbes or
  Cori disease
IV 3p12 <1 Amylo-1,4→1,6 transglucosidase (brancher enzyme) Accumulation of abnormally structured glycogen in liver, MM Severe; death in <48 mo Cirrhosis, late-onset myopathy
  Andersen syndrome
V 11q13 5 Muscle phosphorylase Moderate accumulation of normal structure MM   Cramps on exercise → no ↑blood lactate; myoglobinuria
  McArdle syndrome
VI  
  Hers disease 14q21–q22 Rare Liver phosphorylase Accumulation of normal glycogen in liver   ↓Glucose; may be asymptomatic
VII  
  Tarui disease 12q13.3 25 for VI and VII Phosphofructokinase Enzyme ↓↓↓↓ in MM; ↓50% in RBCs; Accumulation of normal glycogen in MM Adult Hemolysis; cramps on exercise; causes no ↑blood lactate
VIII  
  Hug, Huijing ? Very rare Inactive liver phosphorylase Accumulation of glycogen in liver, CNS Death in childhood  
IXa Xp22.2–p22.1 25 Deficient phosphorylase kinase in liver Glycogen accumulates in liver, RBCs, WBCs    
IXb 16q12–q13     Glycogen accumulates in liver, MM, RBCs, WBCs    
IXc 16p12.1–p11.2   Deficient phosphorylase kinase in liver, testis Glycogen accumulates in liver, RBCs, WBCs    
IXd Xq12–q13   Deficient phosphorylase kinase in muscle Glycogen accumulates in MM    
X ?   cAMP-dependent kinase Glycogen accumulates in liver, MM   Mild hypoglycemia
XI 3q26.1–26.3   Microsomal transport of glucose Glycogen accumulates in liver, proximal renal tubules Galactose intolerance, mild fasting hypoglycemia Proximal renal tubular wasting of PO4, HCO3-
  Fanconi-
  Bickel syndrome
MM, skeletal muscle; CNS, central nervous system; cAMP, cyclic adenosine monophosphate; ↔, variable; ↓ to ↓↓↓↓, degree of decrease.
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  • Establish diagnosis by impaired function of G6P activity in granulocytes and impaired transport protein in liver biopsy.
Type II GSD (Pompe Disease; Generalized Glycogenosis; A-Glucosidase Deficiency)
Type II GSD is an autosomal recessive disease showing absence in infantile onset, or marked reduction in juvenile/adult onset, of lysosomal α-glucosidase (acid maltase) activity. The classic infantile form (type IIA) shows neurologic, cardiac, and muscle involvement; frequent liver enlargement; and death within the first year. The juvenile form (type IIB) displays muscle disease resembling pseudohypertrophic dystrophy, and in the adult form (type IIC), there is progressive myopathy.
Fasting blood sugar, glucose tolerance test, glucagon responses, and rises in blood glucose after fructose infusion are normal. No acetonuria is present.
General hematologic findings are normal.
  • Staining of circulating leukocytes for glycogen shows massive deposition.
  • Confirm diagnosis by absence of α-glucosidase in muscle or liver biopsy or cultured fibroblasts or leukocytes. Assay of amniotic cells or chorionic villus biopsy allows prenatal diagnosis. Neonatal diagnosis may also be possible using dried blood spots.
Type III GSD (Cori-Forbes Disease; Debrancher Deficiency; Limit Dextrinosis)
Type III GSD is an autosomal recessive (gene on chromosome 1p21) disease with enlarged liver, retarded growth, chemical changes, and benign course caused by a deficiency of amylo-1,6-glucosidase (debrancher enzyme). About 80% of those affected lack enzyme in liver and muscle (IIIa), ∼15% lack enzyme only in liver (IIIb); IIIc lacks only enzyme glucosidase and type IIId lacks transferase enzyme only.
Serum creatine kinase (CK) may be markedly increased.
Mild increases in cholesterol and TG are less marked than in type I.
Marked fasting acetonuria (as in starvation).
Fasting hypoglycemia is less severe than in type I.
Normal blood lactate; uric acid is usually normal.
Serum AST and ALT are increased in children but normal in adults.
Diabetic type of glucose tolerance curve, with associated glucosuria.
Infusions of gluconeogenic precursors (e.g., galactose, fructose) causes a normal hyperglycemic response, in contrast to type I.
  • Low fasting blood sugar does not show expected rise after administration of subcutaneous glucagon or epinephrine but does increase 2 hours after high-carbohydrate meal.
  • Confirm diagnosis by deficient debrancher activity in liver and muscle biopsy, WBCs, RBCs, cultured skin fibroblasts. Biochemical findings of increased glycogen, abnormal glycogen structure. Normal phosphorylase and G6P activity.
  • Assay of amniotic cells or chorionic villus biopsy allows prenatal diagnosis.
  • P.622

  • DNA-based diagnosis is available.
Type IV GSD (Andersen Disease; Brancher Deficiency; Amylopectinosis)
Type IV GSD is an extremely rare fatal condition caused by the absence of amylo-(1,4-1,6)-transglucosylase.
Hypoglycemia is not present.
Liver function tests may be altered as in other types of cirrhosis (e.g., slight increase in serum bilirubin, reversed albumin/globulin ratio, increased AST, decreased cholesterol). There may be a flat blood glucose response to epinephrine and glucagon.
  • Biopsy of liver may show a cirrhotic reaction to the presence of glycogen of abnormal structure, which stains with Best carmine and periodic acid–Schiff stain but normal glycogen concentration.
  • Enzyme defect shows in liver, WBCs, cultured fibroblasts.
  • Assay of amniotic cells or chorionic villus biopsy allows prenatal diagnosis.
Type V GSD (Mcardle Disease; Myophosphorylase Deficiency)
Type V GSD is caused by absent myophosphorylase in skeletal muscle; affected persons show very limited ischemic muscle exercise tolerance in the presence of normal appearance of muscle.
Epinephrine or glucagon causes a normal hyperglycemic response.
Biopsy of muscle is microscopically normal in young; vacuolation and necrosis are seen in later years. Increased glycogen is present.
  • Definitive diagnosis is made by absence of phosphorylase.
  • After exercise that quickly causes muscle cramping and weakness, the regional blood lactate and pyruvate do not increase (in a normal person they increase two to five times). A similar abnormal response occurs in type III involving muscle and in types VII, VIII, and X.
Myoglobulinuria may occur after strenuous exercise.
  • Increased serum muscle enzymes (e.g., LD, CK, aldolase) for several hours after strenuous exercise.
Type VI GSD (Hers Disease; Hepatic Phosphorylase Deficiency)
Type VI GSD is a rare disorder caused by a deficiency of hepatic phosphorylase.
Enlarged liver, present from birth, is associated with hypoglycemia.
Serum cholesterol and TGs are mildly increased.
Serum uric acid and lactic acid are normal.
Liver function tests are normal.
Fructose tolerance is normal.
Response to glucagon and epinephrine is variable but tends to be poor.
  • Diagnosis is based on decreased phosphorylase activity in liver, but muscle phosphory-lase is normal.
Type VII GSD (Muscle Phosphofructokinase Deficiency; Tarui Disease)
Type VII GSD is caused by a deficiency of muscle phosphofructokinase, which regulates glycolysis in muscle.
Fasting hypoglycemia is marked.
Other members of family may have reduced tolerance to glucose.
  • RBCs show 50% decrease in phosphofructokinase activity.
  • Biopsy of muscle shows marked decrease (1%–3% of normal) in phosphofructokinase activity and increased glycogen and abnormal morphology. Increased glycogen is found in the brain. Clinically identical to type V.
Type VIII GSD
Type VIII GSD is a very rare X-linked recessive deficiency of phosphorylase kinase with progressive CNS degeneration and enlarged liver.
Blood glucose is markedly decreased, causing hypoglycemic seizures and mental retardation.
Glucagon administration causes no increase in blood glucose (see von Gierke disease), but ingestion of food causes a rise in 2 to 3 hours.
  • Biopsy of liver shows marked decrease in glycogen synthetase.
Type IX GSD
Type IX GSD is usually mild and is caused by a liver phosphorylase kinase deficiency.
May have fasting hypoglycemia that is unusual.
Mild increase in serum AST, ALT, cholesterol, TGs may be present.
Normal uric acid and blood lactate.
Functional tests are not usually useful.
With increasing age, the enzyme deficiency persists, but chemical and clinical abnormalities gradually disappear.
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Porphyrias13
The porphyrias are a group of inherited metabolic disorders caused by enzyme defects in heme synthesis (porphyria cutanea tarda, however, is mainly acquired). Diagnosis is made by patterns of porphyrins and metabolites in urine, stool, RBCs, and plasma; by plasma fluorescence screening; by measuring deficient enzyme; and by genetic testing. More than 80% of heterozygotes are asymptomatic.
Acute episodes (may include abdominal pain and psychiatric symptoms; hypertension, paresthesias, fever, and seizures less frequently; neuromuscular weakness, hyponatremia) are characteristic of acute intermittent porphyria, coproporphyria, and variegate porphyria; may be precipitated by certain drugs (especially barbiturates, alcohol, and sulfonamides; also diphenylhydantoin, chlordiazepoxide, ergots, certain steroids, etc.), infection, starvation. Can be rapidly confirmed by markedly increased urine porphobilinogen (PBG) in single void specimen.
Asymptomatic carriers of acute porphyrias may have few acute attacks throughout life, and levels of ALA, PBG, and porphyrins in urine, serum, and feces are normal in most.
  • Laboratory confirmation may include: 24-hour urine for quantitative 5-aminolevulinic acid, PBG, uroporphyrin, and coproporphyrin (urine should be kept refrigerated, as porphyrins quickly deteriorate, especially at room temperature); plasma porphyrin; free RBC protoporphyrin; spot stool quantitative coproporphyrin and protoporphyrin; Watson-Schwartz test to demonstrate porphyrin precursors in urine (Ehrlich reagent and sodium acetate added to urine; positive turns cherry red with addition of chloroform) is qualitative and lacks sensitivity; evidence of hemolytic anemia or liver disease; fluorescence of appropriate tissues; and enzyme activity assay of RBCs, liver tissue or cultured fibroblasts. Urine δ-ALA and PBG should be measured during episodes. Some drugs may precipitate acute porphyria (stimulate heme synthesis by induction of δ-ALA synthase), e.g., alcohol, antipyretics, barbiturates, estrogens, phenylhydrazine, phenytoin, and sulfonamides.
  • Measurement of enzyme activity and DNA testing help confirm type of porphyria. See Table 12-13.
Footnote
13
Anderson KE, Bloomer JR, Bonkovsky HL, et al. Recommendations for the diagnosis and treatment of the acute porphyrias. Ann Intern Med 2005;142:439–450 [erratum 2005;143(4):316].
Porphyrin Tests of Urine (Fluorometric Methods)
Some drugs that produce fluorescence, e.g., acriflavine, ethoxazene, phenazopyridine, sulfamethoxazole, tetracycline
Classification
Erythropoietic
  • Congenital erythropoietic porphyria (CEP)
  • Erythropoietic protoporphyria
  • Erythropoietic coproporphyria
Hepatic
  • Acute intermittent porphyria (AIP)
  • Variegate porphyria (VP)
  • Hereditary coproporphyria (HC)
  • ALA dehydrase deficiency porphyria
  • Porphyria cutanea tarda (PCT)
Hepatoerythropoietic
  • Hepatoerythropoieic porphyria
(1) Ala Dehydratase Deficiency Porphyria (Porphobilinogen Synthase Deficiency)
ALA dehydrase deficiency porphyria is a very rare autosomal recessive condition with 98% deficiency of enzyme; parents had 50% of normal activity. Acute porphyria-type symptoms are present.
Fig. 12-7. Heme biosynthesis pathway showing site of enzyme action and disease caused by enzyme deficiency. Accumulation of porphyrins and their precursors preceding the enzyme block are responsible for the clinical and laboratory findings of each syndrome. PBG and ALA are increased in all hepatic porphyrias. ALA and PBG cause abdominal pain and neuropsychiatric symptoms. Increased porphyrins (with or without increased PBG or ALA) cause photosensitivity. Thus, deficiencies near the end of the metabolic path cause more photosensitivity and fewer neuropsychiatric findings.
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  • Urine—marked increase in ALA, increased coproporphyrin III (resembles lead intoxication), and uroporphyrin; normal PBG.
  • RBC—ALA dehydrase <5% of normal. Protoporphyrins are increased.
RBC, but not plasma, protoporphyrins are also increased in iron-deficiency anemia and lead intoxication. Screening tests using fluorescence microscopy of RBCs or Wood lamp viewing of treated whole blood may also be positive in iron-deficiency anemia, lead intoxication, and other dyserythropoietic states. In congenital erythropoietic porphyria, 5% to 20% of RBCs show fluorescence that lasts up to a minute or more, in contrast to erythropoietic protoporphyria, where fluorescence is half that and lasts about 30 seconds, and in lead poisoning, where almost all RBCs fluoresce for only a few seconds. Fluorescence of hepatocytes occurs in erythropoietic protoporphyria, PCT, VP, HC.
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Fig. 12-8. Diagnostic strategy (algorithm) for suspected porphyria according to symptoms. Excess production of porphyrins is associated with cutaneous photosensitivity. Excess production of only porphyrin precursors is associated with neurologic symptoms. Excess production of both is associated with both types of clinical symptoms. PBG, porphobilinogens; ALA, aminolevulinic acid; RBC, red blood cells; AIP, acute intermittent porphyria; VP, variegate porphyria; HC, hereditary coproporphyria; PCP, porphyria cutanea tarda; CEP congenital erythropoietic porphyria.
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Table 12-13a. Comparison of Porphyrias
  Enzyme Defect Inheritance, Locationa Usual age at onset Frequency
1. ALA Dehydratase Deficiency Porphyria ALA dehydratase, ∼5% of normal AR 9q34 7 mutations Variable Extremely rare; few reported cases
2. Acute Intermit-tent Porphyria Porphobilinogen deaminase, 50% of normal AD 11q23.3 >227 Rare before puberty Lapland, 1:1,000; elsewhere, 1.5:100,000
3. Congenital Erythropoietic Porphyria Uroporphyrinogen III cosynthase AR 10q25.2–26.3 Fetal life At birth Very rare; <200 reported cases
4. Porphyria Cutanea Tarda Uroporphyrinogen decarboxylase Mostly acquired Also AD 1p34 30s–40s Most common type in United States and Europe
5. Hepatoeryth-ropoietic Porphyria Uroporphyrinogen decarboxylase AR Before age 2y Extremely rare; <20 reported cases
6. Hereditary Coproporphyria Coproporphyrinogen oxidase, 50% of normal AD 3q12 36 mutations Any age Very rare. <50 reported cases
7. Variegate Porphyria Protoporphyrinogen oxidase, 50% of normal AD 1q22 120 mutations Usually 15–30 y South Africa, 3:1,000; rare elsewhere
8. Erythropoietic Protoporphyria Ferrochelatase AD 18q21.3 1–4 y Very rare; <50 reported cases
ALA, aminolevulinic acid; PBG, porphobilinogen; AD, autosomal dominant; AR, autosomal recessive.
aNumber of known mutations.
(2) Acute Intermittent Porphyria14
AIP is the most frequent and severe form of porphyria seen in the United States. It comprises an autosomal dominant (>200 mutations) deficiency of PBG deaminase. Adult onset is usual, with acute attacks of various neuropsychiatric and abdominal symptoms. Patients do not exhibit photosensitivity. It is often precipitated by drugs or hormones.
  • Diagnosed in acute or latent states by finding decreased δ-ALA dehydratase PBG deaminase (∼50% of normal) activity in RBCs and in liver samples, fibroblasts, and lymphocytes; normal in other porphyrias. RBCs may be used to confirm diagnosis, since urine findings may occur during acute attacks of VP and HC.
  • Urine may be of normal color when fresh and becomes red/brown on exposure to sunlight.
  • Urine—Diagnostic finding is marked increase of PBG and, to a lesser extent, of δ-ALA; these decrease during remission but are rarely normal; not increased in silent carriers; also increased in plasma. Watson-Schwartz screening test for PBG should be confirmed by quantitative test. Coproporphyrin and uroporphyrin may be increased.
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Table 12-13b. Comparison of Porphyrias
  Chief Site of Porphyrin Over-production Chief Laboratory Findings
Urine Feces RBCs Plasma
1. ALA Dehydratase Deficiency Porphyria Liver ALA, ↑coproporphyrin, ↑uroporphyrin 0 ALA <5% of normal; ↑protoporphyrin  
2. Acute Intermittent Porphyria Liver Watson-Schwartz positive; darkens on exposure to sunlight; ↑ALAb, ↑uroporphyrin I, ↑PBG constant Porphyrins normal or may be slightly ↑ Porphyrins normal; ↓porphobili-nogen deaminase activity by 50% in 90% of cases Normal or slightly ↑;↑ porphyrins during attacks
3. Congenital Erythropoietic Porphyria Bone marrow Watson-Schwartz negativea ↑uroporphyrin I ↑coproporphyrin ↑coproporphyrin ↑uroporphyrin I and/or zinc porphyrin ↑ uroporphyrin I, coproporphyrin I
4. Porphyria Cutanea Tarda Liver uroporphyrin I >III; pink fluorescence ↑coproporphyrin Porphyrins normal ↑carboxyl-porphyrins
5. Hepatoery-thropoietic Porphyria Bone marrow, Liver Pink urine; ↑carboxyl-porphyrins, ↑porphobili-nogen ↑coproporphyrins, ↑uroporphyrino-gen protoporphyrin (zinc) Normal serum iron
6. Hereditary Coproporphyrin Liver ↑coproporphyrin III; ↑PBG and ↑ALA during attacks Marked ↑coproporphyria III, >↑proto-porphyrin; ↑PBG and ↑ALA during attacks Normal Usually normal
7. Variegate Porphyria Liver ↑coproporphyrin ↑PBG and ↑ALA during attacks; normal otherwise Protoporphyrin, >↑coproporphyrin constant Normal Plasma fluoresence scanning distinguishes it from other porphyrias
8. Erythro-Protoporpoietic Protoporphyria Bone marrow; liver variable Normal porphyrins Protoporphyrin protoporphyrin, Red fluorescence ↑Protoporphyrin
0, absent; ↑, increased; ↑, decreased; >, more than.
aPresent during acute attack; may be absent during remission.
bALA may be increased even more in chronic lead poisoning. Boldface type indicates body material used for diagnosis.
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Table 12-13c. Comparison of Porphyrias
  Clinical Manifestations Precipitated by Comment
Skin Neuro Liver RBCs
1. ALA Dehydratase Deficiency Porphyria 0 4+     Alcohol, stress  
2. Acute Intermittent Porphyria 0 4+ 0   Drugs, hormones  
3. Congenital Erythropoietic porphyria 4+ 0 0 Fluorescent RBCs and normoblasts   Erythrodontia, hemolytic anemia
4. Porphyria Cutanea Tarda 1+ 0 Cirrhosis, hepatitis; ↑iron   Chemicals, iron, alcohol, estrogens. Photosensitivity to sunlight. Diabetes mellitus. 50% have HCV, hepatoma, cirrhosis
5. Hepatoerythropoietic porphyria 4+ 0 1+   Photosensitivity to sunlight Erythrodontia, normochromic anemia.
6. Hereditary Coproporphyria 1+ 1+ ↑ALA synthase   Drugs, especially barbiturates. Photosensitivity to sunlight.  
7. Variegate Porphyria 3+ 4+ 0   Estrogens, barbiturates. Photosensitivity to sunlight.  
8. Erythropoietic Protoporphyria 3+ 0 1+ 1+   Anemia is unusual
0, absent; 1+ to 4+, degree of severity; HCV, hepatitis C virus.
Stool—protoporphyrin and coproporphyrin are usually normal; may be slightly increased.
During acute attack, there may be decreased serum sodium (may be marked), chloride, and magnesium, increased BUN, and slight leukocytosis.
Liver function tests are normal.
Other frequent laboratory abnormalities are increased serum cholesterol, hyperbeta-lipoproteinemia (type IIa), increased serum iron, abnormal glucose tolerance, and increased T-4 and thyroxine-binding globulin without hyperthyroidism.
Footnote
14
von und zu Fraunberg N, Pischik E, Udd L, et al. Clinical and biochemical characteristics and genotype-phenotype correlation in 143 Finnish and Russian patients with acute intermittent porphyria. Medicine (Baltimore) 2005;84:35–47.
(3) Congenital Erythropoietic PORPHYRIA
CEP is an extremely rare, autosomal recessive disorder caused by decreased activity of uroporphyrinogen III cosynthase in RBCs, causing overproduction of uroporphyrinogen I and coproporphyrinogen, which have no role in heme synthesis, but their oxidation causes findings listed in the following. The usual onset of CEP is in infancy; patients exhibit extreme cutaneous photosensitivity with mutilation and red urine and teeth.
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  • Ultraviolet fluorescence of variable number of RBCs and normoblasts; also urine, teeth, and bones.
Normocytic, normochromic, anicteric hemolytic anemia that tends to be mild; may be associated with hypersplenism and increased reticulocytes and normoblasts.
  • Urine—marked increase of uroporphyrin I is characteristic; coproporphyrin shows lesser increase. Excretion of PBG and δ-ALA is normal. Watson-Schwartz test is negative.
  • RBCs—increased uroporphyrins I and/or zinc protoporphyrins.
  • Plasma—marked increase of uroporphyrins; increased coproporphyrin.
  • Stool—marked increase of coproporphyrins.
(4) Porphyria Cutanea Tarda
PCT is the most common porphyrin disorder. It is caused by a deficiency (∼50%) of uroporphyrinogen decarboxylase. It is basically an acquired disorder (inhibitor of uroporphyrinogen decarboxylase may be generated in liver) that may be caused by hepatoma, cirrhosis, or chemicals (e.g., an epidemic in Turkey was caused by contamination of wheat by hexachlorobenzene). The disease may be activated by increased ingestion of iron, alcohol, or estrogens.
The inherited form (autosomal dominant) is expressed in ∼20% of patients with this gene and is caused by a deficiency of uroporphyrinogen decarboxylase in liver in toxic/sporadic forms (type I) and in all tissues in familial form (type II). Associated with alcoholic liver disease and hepatic siderosis.
  • Urine—marked increase of uroporphyrin (frequently up to 1,000 to 3,000 μg/24 h [normal <300 μg]) with only slight increase of coproporphyrin and ratio of uroporphyrin/coproporphyrin >7.5 (ratio <1 in VP). In biochemical remission, 24-hour uroporphyrin is <400 μg.
Stool—isocoproporphyrins are present.
Plasma—increased protoporphyrin.
RBC porphyrins are normal.
  • Distinguished from VP, in which there is increased fecal protoporphyrins and urine coproporphyrins exceed uroporphyrins during cutaneous symptoms.
Serum ferritin, iron, and transferrin saturation are increased in ∼50% of cases.
Laboratory findings of underlying liver disease; ∼50% have hepatitis C. Liver biopsy shows morphologic changes of underlying disease and fluorescence under ultraviolet light; usually shows iron overload.
Diabetes mellitus in ≤33% of patients due to associated hemochromatosis.
Phlebotomy therapy to remove iron is monitored by decreased urinary excretion of uroporphyrins.
(5) Hepatoerythropoietic Porphyria
Hepatoerythropoietic porphyria is an extremely rare (few reported cases) autosomal recessive severe deficiency of uroporphyrinogen decarboxylase. Onset occurs before age 2 years.
  • Marked deficiency of uroporphyrinogen decarboxylase (5%–10% of normal; 50% of normal in parents).
  • Pink urine, increased uroporphyrinogens I, III.
  • RBCs contain increased zinc protoporphyrin.
Plasma contains increased uroporphyrin.
  • Porphyrin abnormalities resemble porphyria cutanea tarda but additionally zinc protoporphyrin is increased in RBCs.
Mild normochromic anemia; fluorescent normoblasts in bone marrow. Normal serum iron.
Increased serum GGT and transaminase may occur. Liver disease may progress to cirrhosis.
Severe skin involvement. Pink teeth.
(6) Hereditary Coproporphyria
HC is a very rare autosomal dominant deficiency of coproporphyrinogen oxidase. Two-thirds of patients are latent. It is precipitated by the same factors as is AIP.
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  • Stool—coproporphyrin III is always increased—very markedly during an acute attack; coproporphyrin III is also increased in plasma. Protoporphyrin is normal or only slightly increased.
Urine—coproporphyrin III may be increased or not; is usually normal during remission. Isolated increase may be secondary to liver, hematologic, neoplastic, and toxic conditions. Increased PBG and to a lesser extent ALA during acute attacks.
  • RBCs—diminished coproporphyrinogen oxidase is strongly indicative.
  • Liver—diminished coproporphyrinogen oxidase is diagnostic; increased ALA synthase.
(7) Variegate Porphyria15
VP is an autosomal dominant condition caused by a deficiency of protoporphyrinogen oxidase (by ∼50%), which can also be found in cultured fibroblasts, liver tissue, and peripheral blood lymphocytes. Skin or neurologic manifestations may occur. VP is precipitated by the same factors as is AIP.
  • Plasma fluorescence scanning at 625 nm efficiently distinguishes VP from other porphyrias. Plasma scanning is more sensitive and specific than fecal testing, but neither is sensitive in children and both are less sensitive in asymptomatic carriers.
  • Stool chromatography—characteristic change is marked increase of protoporphyrin, which is found during attack, remission, or only with skin manifestations. When stool is normal or borderline or in asymptomatic patients, can demonstrate increased porphyrins in bile.
Urine—marked increase of δ-ALA and PBG during an acute attack; levels are usually normal after acute episode, in contrast to AIP and HC.
Blood—porphyrin levels are not increased.
  • DNA analysis for the appropriate gene mutation is preferred to identify carriers, especially children.
Footnote
15
Hift RJ, Davidson BP, van der Hooft C, et al. Plasma fluorescence scanning and fecal porphyrin analysis for the diagnosis of variegate porphyria: precise determination of sensitivity and specificity with detection of protoporphyrinogen oxidase mutations as a reference standard. Clin Chem 2004;50:915–923.
(8) Erythropoietic Protoporphyria
Erythropoietic protoporphyria is a relatively common type of porphyria caused by an autosomal dominant deficiency of ferrochelatase activity in bone marrow, reticulocytes, liver, and other cells.
Mild microcytic hypochromic anemia in 20% to 30% of patients.
Laboratory findings due to liver disease (severe in 10% of cases) with increased serum direct bilirubin, AST, and ALP (due to intrahepatic cholestasis), and gallstones containing porphyrins may be found.
Urine—porphyrins within normal limits.
  • RBCs—marked increase of free protoporphyrin in symptomatic patients (zinc-chelated form may also be increased in iron-deficiency anemia and lead poisoning, but nonchelated form is present in protoporphyria). May be normal or slightly increased in asymptomatic carriers. Examination of dilute blood by fluorescent microscopy may show rapidly fading fluorescence in variable part of RBCs.
  • Stool—protoporphyrin is usually increased in symptomatic patients and in some carriers, even when carrier RBC porphyrins are normal.
  • Three chemical patterns consist of increased free RBC and stool protoporphyrin alone or with each other.
Lysosomal Storage Disorders
Lysosomes are acidic organelles containing hydrolases that normally degrade larger molecules. Lysosomal storage diseases are a group of >50 inherited diseases due to deficient activity of these enzymes causing abnormal accumulation of substrates. Clinical syndromes depend on different organ accumulations and lysosome-associated protein, neonatal, juvenile, and adult onsets.
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Lysosomal Storage Disorder Sphingolipidoses Deficient Enzyme Stored Material Chief Sites of Involvement
GM1and GM2 β-galactosidase GM1 ganglioside CNS
Tay-Sachs Hexosaminidase A GM2 ganglioside, other metabolites CNS
Sandhoff Hexosaminidase B GM2 ganglioside, other metabolites CNS
Gaucher types Glucocerebrosidase (acidic β-glucosidase Glucocerebroside CNS, spleen, liver, bones
Niemann-Pick types A, B Sphingomyelinase Sphingomyelin CNS, liver, spleen, lungs; no CNS in type A
Niemann-Pick type C, D Mutant protein leading to block in cholesterol esterification. Sphingomyelinase not deficient. ? CNS, liver,
Krabbe (globoid cell leukodystrophy) β-galactosylceramidase   CNS, peripheral NS
Metachromatic leukodystrophy Arylsulfatase A Cerebroside sulfate CNS, peripheral NS
Multiple sulfatase deficiency Various sulfatases Sulfate-containing glycolipids, MPS, steroids CNS, spleen, liver, bones
Fabry disease α-galactosidase A Ceramide trihexoside Skin, peripheral NS, kidney, eye, heart and brain vessels
Mucopolysaccharidoses see Table 12-14
MPS IH (Hurler syndrome) α-L-iduronidase Dermatan sulfate, heparan sulfate CNS, bone liver, heart
MPS IS (Scheie syndrome) α-L-iduronidase Dermatan sulfate, heparan sulfate Eye, bone, heart
MPS IH/IS (Hurler/Scheie) α-L-iduronidase
MPS II (Hunter syndrome) Iduronate sulfatase Dermatan sulfate, heparan sulfate CNS, bone liver, heart
MPS III, Sanfilippo type A Heparan N-sulfatase Heparan sulfate CNS, bone
MPS III, Sanfilippo type B N-acetyl-α-D-glucosaminidase
MPS III, Sanfilippo type C Acetyl-CoA: α-glucosaminide-N-acetyltransferase
MPS III, Sanfilippo type D N-acetylglucosamine-6-sulfatase
MPS IV, types A, B (Morquio syndrome) Type A: N-acetyl-galactosamine-6-sulfate sulfatase
Type B: β-galactosidase (specific for keratan sulfate)
Keratan sulfate Bone
MPS VI (Maroteaux-Lamy) Arylsulfatase B Dermatan sulfate Bone
MPS VII (Sly syndrome) β-glucuronidase Dermatan sulfate, heparan sulfate Bone, liver, CNS
MPS IX hyaluronidase deficiency Hyaluronidase
Sphingolipidoses Mucopolysaccharidoses
Mucolipi-doses (Oligosacchari-doses)
Sialidosis type I and II α-neuroaminidase Sialooligosaccharides CNS, peripheral NS, eye, skin
Mannosidosis Mannosidase Oligosaccharides CNS, mild bone changes, hepatosplenomegaly
Fucosidosis types I, II Fucosidase Oligosaccharides, sphingolipids CNS, high sweat electrolytes
Aspartylglycosa-minuria Aspartyl-glucosa-minidase Glycoasparagines  
Mucolipidosis II (I-cell disease) (formerly MPS VII) N-acetylglucosamine-1-P-transferase   CNS, bone, connective tissue
Mucolipidosis III (Pseudo-Hurler polydystrophy) N-acetylglucosamine-1-P-transferase   Predominant-ly joint and connective tissue
Mucolipidosis IV (ML IV)   Gangliosides, glycosaminoglycans CNS, eye
Lysosomal Efflux
Cystinosis ?   Kidney
Salla disease ?   CNS
Chédiak-Higashi syndrome (see Chapter 11)
GM1, GM2, gangliosides 1 and 2; CNS, central nervous system; MPS, mucopolysaccharidosis.
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Cystinosis16
Cystinosis is an autosomal recessive lysosomal storage disease caused by impaired transport of cystine from lysosomes to cytoplasm; this causes abnormal accumulation of soluble and crystalline cystine amino acid in various organs. It is mapped to chromosome 17p13; there are >50 mutations.
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Table 12-14. Classification of Mucopolysaccharidoses
Type of Mucopolysaccharidosis (clinical name) Deficient Enzyme Mucopolysaccharide Excreted in Urine Signs/Symptoms
IH (Hurler’s syndrome) Alpha-L-iduronidase Dermatan sulfate and heparan sulfate in 7:3 ratio Progressive mental/physical disability from 1 yr of age; hyperplastic gums; coarse face; stiff joints (clawhands); organomegaly; dwarfing; dysostosis multiplex
IS (Scheie’s syndrome) Alpha-L-iduronidase Dermatan sulfate and heparan sulfate Mild form of MPS I; mild or no mental retardation; clawhands; aortic stenosis
IH/S (Hurler-Scheie syndrome) Aplha-L-iduronidase   Features intermediate between Hurler’s and Scheie’s syndromes
II (Hunter’s syndrome) Iduronate sulfatase Dermatan sulfate and heparan sulfate Dysostosis multiplex; mild to severe mental retardation; no corneal opacity; longer life compared with MPS I
IIIA (Sanfilippo’s syndrome, type A) Heparan N-sulfatase (sulfamidase) Heparan sulfate Mild or no connective tissue abnormalities; marked hirsutism; behaviorism progresses to severe mental retardation; no corneal opacity
IIIB (Sanfilippo’s syndrome, type B) Alpha-N-acetylglu-cosaminidase (alpha-hexosaminidase) Heparan sulfate Same as in MPS IIIa
IIIC (Sanfilippo’s syndrome, type C) Acetyl CoA: alpha-glucosaminide N-acetyltransferase Heparan sulfate Same as in MPS IIIa
IIID (Sanfilippo’s syndrome, type D) N-Acetylglucosamine-6-sulfatase Heparan sulfate Same as in MPS IIIa
IVA (Morquio’s syndrome, type A N-Acetylgalactosamine-6-sulfatase Keratan sulfate Marked skeletal abnormalities; small stature; short neck; prominent lower ribs; normal intellect; coma
IVB (Morquio’s syndrome, type B) Beta-galactosidase Keratan sulfate  
V This class is vacant now (formerly was Scheie’s syndrome)    
VI (Maroteaux-Lamy syndrome) N-Acetylgalactosamine-4-sulfatase (arylsulfatase B) Dermatan sulfate Severe dysostosis multiplex and corneal opacity; retarded growth; normal intellect; cardiac abnormalities; a mild form also occurs
VII (Sly’s syndrome)   Beta-glucuronidase Dermatan sulfate, heparan sulfate, chondroitin 4, 6-sulfate Mild mental retardation; organomegaly; corneal opacity may occur; coarse facies; gingivitis; very heterogeneous clinical appearance
CoA = coenzyme A; MPS = mucopolysaccharidosis.
Inheritance in Hunter’s syndrome is X-linked recessive; others are autosomal recessive.
Cloudy cornea in IH, IS, IVA, IVB, VI, VII.
Mental retardation in IH, II, IIIA, IIIB, IIIC, IIID, VII.
Hepatosplenomegaly in IH, II, IIIA, IIIB, IIIC. IIID, IVB, VI, VII.
Skeletal defects in all.
Footnote
16
Gahl WA, Thoene JG, Schneider JA. Cystinosis. N Engl J Med 2002;347:111–121.
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Infantile (acute nephropathic form)
Renal Fanconi syndrome (aminoaciduria, glycosuria, proteinuria, renal tubular acidosis, phosphaturia, hypophosphatemic rickets) and also glomerular disease, leading to end-stage renal disease by age 10 years.
Polyuria: 2 to 6 L/d (<300 mOsm/L) may cause dehydration with loss of electrolytes.
  • Prenatal diagnosis by testing cultured amniocytes or chorionic villus.
  • Neonatal diagnosis is performed by measuring cystine in leukocytes or placenta.
Crystalline inclusions in conjunctiva, cornea (slit lamp examination confirms diagnosis after 1 year of age) and leukocytes, bone marrow, rectal mucosa. Biopsy is not required for diagnosis.
Late manifestations: type 1 diabetes mellitus, pancreatic insufficiency, primary testicular failure, hypothyroidism, myopathy, etc.
Juvenile (late onset) has much lower progression of nephropathic disease.
Adults/benign disease may show
Only cystine crystals in cornea
Urinary tract calculi
Cystinuria (cystine crystals in urine; >200 mg of cystine in 24-hour urine)
Asymptomatic
Sphingolipidoses
Tay-Sachs Disease (GM2 Gangliosidosis, Type I)
Tay-Sachs disease is an autosomal recessive (chromosome 15) lysosomal storage disease found predominantly in Ashkenazi Jews, French Canadians, and Cajuns, characterized by appearance in infantile form by psychomotor deterioration, blindness, cherry-red spot in the macula, and an exaggerated extension response to sound, with death by age 4; juvenile form (with death by age 15), and chronic form in adults. Macula spots appear only in the infantile form.
  • Diagnosis is established by absence of hexosaminidase A activity in serum, plasma, leukocytes, and cultured skin fibroblasts (also absent in all tissues of body and tears). Accumulation of ganglioside 2 (GM2) in the brain is caused by a deficiency or absence of hexosaminidase A.
  • Heterozygotes can be identified by plasma assay showing 50% decrease in activity of hexosaminidase A; screening should be done before pregnancy, which may cause false-positive results; oral contraceptives, diabetes mellitus, and liver disease may also cause false-positive results; in these cases, WBCs are used for hexosaminidase A assay.
  • Prenatal diagnosis using cultured amniotic cells is superior to that done using amniotic fluid or uncultured amniotic cells; false-negative results can occur because of contamination with maternal blood or tissue or bacteria.
  • PCR for specific DNA mutations in WBCs or fibroblasts is more specific than enzyme assay, can detect various mutations, and can predict severity of disease in affected child.
There is early marked increase of serum LD and AST, which return to normal if patient survives 3 to 4 years.
Decrease in serum fructose-1-phosphate aldolase; also decreased in heterozygotes.
CSF AST parallels serum AST.
Occasional vacuolated lymphocytes are seen.
Liver function tests are normal.
Serum acid phosphatase is normal.
  • Electron microscopy shows characteristic cytoplasmic bodies in brain. (In Sandhoff disease [similar to Tay-Sachs disease] total deficiency of β-hexosaminidase, glyco-lipids, and other substances accumulate in brain as well as other tissues.)
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Table 12-15. Classification of Sphingolipidosis
Clinical Name Enzyme Defect Specimen for Assay Major Lipid Accumulation Signs/Symptoms
Gaucher’s disease Cerebroside beta-glucosidase in L, F Glucosyl ceramide Enlarged spleen and liver; erosion of long bones and pelvis; mental retardation only in infantile form
Niemann-Pick disease Sphingomyelinase in F, U, S Sphingomyelin Enlarged liver and spleen; mental retardation; ∼30% have cherry-red spot in retina
Krabbe’s disease (globoid cell leukodystrophy) Cerebroside beta-glucosidase in F, L, A, S Galactosyl ceramide X-linked; mental retardation; almost total absence of myelin; globoid bodies in brain white matter; increased CSF protein
Metachromatic leukodystrophy Arylsulfatase A in L, U, F, S Sulfatide Mental retardation; psychological disturbances in adult form
Multiple, sulfatase deficiencies Arylsulfatase A, B, C in F, L Sulfatide Resembles metachromatic leukodystrophy; dermatan sulfate and heparan sulfate increased in urine
Ceramide lactoside lipidosis Beta-galactosidase in L, S Ceramide lactoside Slowly progressive brain damage; enlarged liver and spleen
Fabry’s disease (angio-keratoum corporis diffusum universale) Alpha-galactosidase in S, L, F, U, T Trihexosyl ceramide Skin lesions; loss of renal function; involvement of heart, and brain vessels; pain in lower limbs; cherry-red spot in retina
GM2 gangliosidosis  
  Tay-Sachs disease Hexosaminidase A in S, L, A, F, U, T Gangliositle GM2 Mental retardation; cherry-red spot in retina: blindness; muscle weakness
  Sandhoff’s disease Hexosaminiriase A, B in S, T, A, F, U, T Ganglioside GM3 and globoside Clinical picture same as in Tay-Sachs disease but mild peripheral neuropathy and organomegaly
Landing’s disease (GM1 gangliosidosis) Lysosomal acid-beta-galactosidase in L, F, U Ganglioside GM1 Psychomotor deterioration; cherry-red spot in retina; enlarged liver and spleen; dysostosis multiplex
Farber’s lipogranu-lomatosis* Acid ceramidase in L, F Ceramide Granulomas of dermis and viscera; joint disease in infancy
Fucosidosis Alpha-fucosidase in L H-isoantigen  
Lactosyl ceramidosis Neutral beta-galactosidase in F Lactosyl ceramide  
A = amniocytes; F = fibroblasts; L = leukocytes; S = serum; U = urine; T = tears; CSF = cerebrospinal fluid.
Note: Molecular techniques are now available for diagnosis of Gaucher’s, Niemann-Pick, Tay-Sachs, Sandhoff’s, Fabry’s, and Wolman’s diseases and for generalized gangliosidosis.
*Diagnosis confirmed by biopsy of subcutaneous nodules rather than by determination of enzyme activity.
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Fabry Disease (α-Galactosidase A Deficiency)17
Fabry disease is a rare X-linked recessive lysosomal storage disease caused by a deficiency of α-galactosidase A (α-gal A) that results in progressive accumulation of globotriaosylceramide (Gb2) and related glycosphingolipids in plasma and vascular endothelium, leading to ischemia and infarction in various organs (e.g., kidney, heart, brain, eye, nerves) and characteristic angiokeratomas of skin. Carrier females may have mild or severe disease. The gene for the disease is located on chromosome Xq22.
  • Absent (<1%) α-gal A in plasma and leukocytes in classical form and <10% of normal in cardiac variant in males. In female carriers, may be very low or normal; therefore must demonstrate the specific family genetic mutation (of >300 mutations).
  • Heterozygote detection by enzyme assay of cultured cells or by assay of Gb2 content of 24-hour urine sediment.
  • Urine lipid profiles by MS/MS (including various ceramides) may be useful for identifying hemizygotes and heterozygotes.18
  • Prenatal diagnosis by demonstration of XY karyotype and enzyme deficiency in cultured amniotic fluid cells or chorionic villi. If family mutation is known, molecular studies can replace or confirm enzymatic diagnosis.
  • Laboratory findings due to Gb2 accumulation in vascular endothelium and organs, especially of kidneys (e.g., renal failure), heart (e.g., mitral valve disease left ventricular hypertrophy), and brain (e.g., stroke).
Patients with blood group B antigen (a glycosphingolipid) may have a more severe prognosis.
Footnote
17
Desnick RJ, Brady R, Barranger J, et al. Fabry disease, an under-recognized multisystemic disorder: expert recommendations for diagnosis, management, and enzyme replacement therapy. Ann Intern Med 2003;138:338.
18
Fuller M, Sharp PC, Rozaklis T, et al. Urinary lipid profiling for the identification of Fabry hemizygotes and heterozygotes. Clin Chem 2005;51:688–694.
Gaucher Disease
Gaucher disease is an autosomal recessive deficiency of glucocerebrosidase (glucosylceramidase), which causes deposition of glucocerebroside in cells of macrophage-monocyte system. It is the most frequent lipid storage disease and may be present in 10,000 to 20,000 Americans, with the highest prevalence of type 1 in Ashkenazi Jews. The gene is located on chromosome 1q21.
  • Decreased β-glucocerebrosidase activity in leukocytes or fibroblasts is reliable diagnostic method; substantial overlap between heterozygotes and normal persons. Confirmed by DNA testing.
  • Diagnostic Gaucher cells are seen in bone marrow aspiration or in needle biopsy or aspiration of spleen, liver, or lymph nodes examined for thrombocytopenia or unrelated disorder and cause the nonneurologic manifestations.
  • Serum acid phosphatase is increased in most patients (substrate for test is different from that for prostatic acid phosphatase; i.e., uses phenyl phosphate or p-nitrophenylphosphate instead of glycerophosphate). It may return to normal following splenectomy.
Serum angiotensin-converting enzyme is increased in most patients.
Serum cholesterol and total fats are normal.
Laboratory findings due to involvement of specific organs
  • Spleen—hypersplenism occurs with anemia (normocytic normochromic), leukopenia (with relative lymphocytosis; monocytes may be increased), thrombocytopenia without bleeding.
  • Bone—serum ALP may be increased; osteopenia.
  • Liver—serum AST may be increased.
  • Lung infiltrates
  • CNS involvement only in types 2 and 3; AST may be increased in CSF.
Laboratory findings due to increased incidence of lymphoproliferative disorders (e.g., multiple myeloma, chronic lymphocytic leukemia).
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  • Prenatal diagnosis by enzymatic determination of cultured amniotic fluid cells. If both parental mutations have been identified by DNA, chorionic villus sampling for fetal DNA can be done.
  • Carrier identification by enzymatic methods are confirmed by DNA.
  • Phenotype cannot be predicted from genotype. Common mutations can be detected using PCR and aid in genetic counseling for general risk of transmitting the gene but not specific prognosis for future affected children.
Type 1 (99% of patients): adult; no neurologic involvement.
Type 2: fulminating disorder with severe neurologic involvement and death within first 18 months.
Type 3: juvenile form with later onset of neurologic symptoms and milder course, with death in early childhood.
Bone marrow transplantation is effective therapy but has associated morbidity and mortality. Enzyme replacement therapy usually obviates need for splenectomy.
Niemann-Pick Disease
Niemann-Pick disease is a syndrome of autosomal recessive traits causing accumulation of sphingomyelin and cholesterol in lysosomes of macrophage-monocyte system. There are four major subtypes.
  • Diagnosis by demonstrating sphingomyelinase deficiency in cultured fibroblasts or circulating leukocytes: 1% to 10% of normal in types A and B; 50% to 75% of normal in types C and D.
  • Diagnosis of types C and D by showing biochemical defect in cholesterol transport in cultured fibroblasts.
  • Heterozygote identification of types A and B by DNA analysis. Heterozygote identification of types C and D not available.
  • Foamy histiocytes (Niemann-Pick [NP] cells) may be found in bone marrow aspiration and in liver, spleen, skin, skeletal muscle, and eye, and may appear in peripheral blood terminally; not pathognomic.
Peripheral blood lymphocytes and monocytes may be vacuolated (2%–20% of cells).
WBC count is variable.
Rectal biopsy may show changes in ganglion cells of myenteric plexus.
Laboratory findings due to involvement of specific organs:
  • Anemia is caused by hypersplenism or microcytic anemia associated with anisocytosis, poikilocytosis, and elliptocytosis.
  • AST may be increased in serum and CSF.
  • Enzyme changes in CSF are same as in Tay-Sachs disease, except that LD is normal.
Acid phosphatase is increased (same as in Gaucher disease).
LD is normal in serum and CSF.
Different enzyme activities result in different clinical forms.
  • Type A: acute progressive neuropathic loss of motor and intellectual function early in life, with death common in infancy. Cherry-red macula is often present. Enlarged liver and spleen.
  • Type B similar to type A but later onset and not neuropathic.
  • Type C may have prolonged neonatal jaundice; variable CNS; less severe liver and spleen enlargement.
  • Type D: not neuropathic; later onset.
  • Prenatal diagnosis of types A and B by measuring acid sphingomyelinase activity in cultured amnoicytes or chorionic villi.
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GM1 Gangliosidosis (Landing Disease; Systemic Late Infantile Lipidosis)
GM1 gangliosidosis is a rare autosomal recessive deficiency of acid β-galactosidase with no racial predilection characterized by psychomotor deterioration, enlargement of liver and/or spleen, cherry-red macular spots, and dysostosis multiplex. There are infantile, juvenile, and adult forms.
  • Diagnosis by absence of lysosomal acid β-galactosidase enzyme in leukocytes, cultured fibroblasts, or brain. Tissue biopsy or culture of marrow or skin fibroblasts shows accumulation of ganglioside GM1; also can demonstrate GM1 in brain and viscera and mucopolysaccharides in viscera.
  • Heterozygote carriers can be detected by enzyme assay in leukocytes.
  • Abnormal leukocytic granulations (Alder-Reilly bodies) may be present. Vacuolated lymphocytes may be found.
  • Foam cell histiocytes (resembling Niemann-Pick cells) may be seen in biopsy from bone marrow, liver, or rectum.
  • Prenatal diagnosis by enzyme assay in cultured amniotic fluid cells or by HPLC analysis of galactosyl oligosaccharides in amniotic fluid.
Serum LD, AST, and fructose-1-phosphate aldolase are normal.
Mucolipidoses
I-cell Disease (Mucolipidosis II)
I-cell disease is an autosomal recessive deficient activity of N-acetylglucosamine 1-phosphotransferase, which causes deficiency of multiple lysosomal enzymes. Clinical features resemble Hurler syndrome, but without corneal changes or increased mucopolysaccharides in urine.
  • Deficiency of N-acetylglucosaminylphosphotransferase in cultured fibroblasts establishes the diagnosis.
  • Vacuolation (cytoplasmic inclusions on phase contrast microscopy) in lymphocytes, fibroblasts, liver and kidney cells, which are positive for Sudan and acid phosphatase. Lysosomal enzyme activity (hexosaminidase A and B and α-galactosidase) is low in these cells but high in serum or culture medium.
  • Prenatal diagnosis by high levels of multiple acid hydrolases in amniotic fluid or deficiency of them in cultured amniocytes.
Some heterozygotes have abnormal inclusions in fibroblasts. Some heterozygotes may have intermediate enzyme levels in leukocytes and cultured fibroblasts.
Urine mucopolysaccharides are not increased.
Mucolipidosis III (N-Acetylglucosaminylphosphotransferase Deficiency; Pseudo-Hurler Dystrophy)
The clinical features of type III mucolipidosis resemble those of Hurler syndrome but without increased mucopolysaccharides in urine.
  • Autosomal recessive transmission of fundamental defect in recognition or catalysis and uptake of certain lysosomal enzymes due to deficient activity of N-acetylglucosamine-1-transferase.
  • Heterozygotes may have intermediate enzyme levels in leukocytes and cultured fibroblasts.
Mucopolysaccharidoses, Genetic
The mucopolysaccharidoses (MPSs) are chronically progressive, clinically heterogeneous diseases resulting from defects in stepwise degradation of mucopolysaccharides caused by enzyme blocks in catabolism of keratin, heparin, or dermatan. See Table 12-14.
  • All MPSs show metachromatically staining inclusions of mucopolysaccharides in circulating polynuclear leukocytes (Reilly granulations) or lymphocytes, cells of inflammatory exudate, and bone marrow cells (most consistently in clasmatocytes). Mucopolysaccharide is also deposited in various parenchymal cells. Detection of deficiency of lysosomal enzyme in cultured fibroblasts establishes the diagnosis and makes prenatal diagnosis possible. Serum can be used for diagnosis in MPS II, IIIB, and VI. Leukocytes can be used for diagnosis in MPS IH, IS, IIIA, and IIIC. RBCs can be used for diagnosis in III, IV, and VI. Enzyme deficiency is demonstrable in liver in all except V and VII; demonstrable in muscle in all except IH and II. Increased glycogen in affected organs except in IV; glycogen structure is normal except in III and IV. Carrier state detection of IH, III, IV, and VI is not reliable because of overlapping with normal persons of enzymatic activity values.
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Inheritance in Hunter syndrome is X-linked recessive; all others are autosomal recessive.
Cloudy cornea in IH, IS, IVA, IVB, VI, and VII.
Mental retardation in IH, II, IIIA, IIIB, IIIC, IIID, and VII.
Hepatosplenomegaly in IH, II, IIIA, IIIB, IIIC, IIID, IVB, VI, and VII.
Skeletal defects in all.
Hurler Syndrome (Mucopolysaccharidosis IH)
Hurler syndrome is a lysosomal disorder caused by deficient activity of α-L-iduronidase Most with the disorder die by age 10 years.
  • Initial diagnosis by quantitative increase of mucopolysaccharides in urine; confirmed by assay of α-L-iduronidase in cultured fibroblasts or leukocytes.
Similar enzyme assay detects carriers who have ∼50% activity, but the wide range with overlap between normal and carriers may make the diagnosis difficult in individual cases.
  • Prenatal diagnosis by assay of enzyme or mucopolysaccharides in amniocytes or chorionic villi sampling.
Hunter Syndrome (Mucopolysaccharidosis II)
Hunter syndrome is clinically similar to Hurler syndrome but milder, with no corneal opacity.
  • Initial diagnosis by quantitation of total glucosaminoglycans in urine and accumulation of keratan sulfate in tissues is confirmed by enzyme assay in fibroblasts.
  • Heterozygous female carriers recognized by MPS in fibroblasts or enzyme assay in individual hair roots.
  • Prenatal diagnosis by enzyme assay of amniotic fluid should be confirmed by assay of cultured cells.
  • Maternal serum shows increased activity of iduronate sulfate sulfatase with a normal or heterozygous fetus but no increase if fetus has Hunter syndrome.
Mild and severe subtypes
Sanfilippo Type A Syndrome (Mucopolysaccharidosis III)
The four types of Sanfilippo syndrome cannot be distinguished clinically.
  • Only MPS in which heparan sulfate is found in urine, which confirms diagnosis.
  • Assay of fibroblasts shows deficiency of enzyme in patient and decrease of normal activity in carrier who also show mucopolysaccharide accumulation.
  • Metachromatic inclusion bodies in lymphocytes are coarser and sparser than in Hurler syndrome and may be seen in bone marrow cells. Severe cerebral changes with relatively mild changes in other body tissues.
Morquio Syndrome (Mucopolysaccharidosis IV)
  • Keratan sulfate is increased in urine (often 2×–3× normal).
  • Metachromatic granules may be seen in polymorphonuclear leukocytes.
  • Diagnosis by enzyme assay in fibroblasts and leukocytes.
  • Prenatal diagnosis by assay of enzymes in cultured amniocytes.
Maroteaux-Lamy Syndrome (Mucopolysaccharidosis VI)
  • Metachromatic cytoplasmic inclusions (Alder granules) may be seen in 50% of lymphocytes and 100% of granulocytes are more marked than in other MPSs.
  • Large amount of dermatan sulfate occurs in urine.
  • Diagnosis is established by deficiency of specific enzyme in cultured fibroblasts.
  • Enzyme assay also allows diagnosis of heterozygotes and prenatal diagnosis.
Other rare diseases due to enzyme deficiencies that resemble these conditions include I-cell disease (mucolipidosis I) and mucolipidosis III and related disorders.
Leukodystrophies
The leukodystrophies are autosomal or x-linked inherited disorders of myelination that cause destruction or abnormal formation of nervous system white
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matter. This category also includes Canavan disease, adrenoleukodystrophy, and others.
Metachromatic Leukodystrophy
Metachromic leukodystrophy is a rare autosomal recessive lipidosis caused by a deficiency of arylsulfatase A. There are infantile and adult forms with inability to degrade sphingolipid, sulfatide, or galactosylceramide, causing accumulation of sulfatide.
  • Urine sediment may contain metachromatic lipids (from breakdown of myelin products).
CSF protein may be normal or increased ≤200 mg/dL.
  • Biopsy of dental or sural nerve stained with cresyl violet showing accumulation of metachromatic sulfatide is diagnostic. Also increased in brain, kidney, liver.
  • Conjunctival biopsy shows metachromatic inclusions within Schwann cells.
Krabbe Disease (Globoid Cell Leukodystrophy)
Krabbe disease is an autosomal recessive deficiency of galactosylceramidase mapped to chromosome 14, which causes progressive disease of CNS myelination from ∼3 months of age, ending in death by ∼2 years.
  • Diagnosis by deficiency of this enzyme (5%–10% of normal) in leukocytes or cultured fibroblasts.
  • Conjunctival biopsy shows characteristic ballooned Schwann cells.
  • Brain biopsy (massive infiltration of unique multinucleated inclusion-containing globoid cells in white matter due to accumulation of galactosylceramide; also diffuse loss of myelin, severe astrocytic gliosis).
CSF protein electrophoresis shows increased albumin and α-globulin and decreased β- and γ-globulin (same as in metachromatic leukodystrophy).
  • Prenatal diagnosis by measuring enzyme activity in cultured amniotic fluid cells.
Other Genetic Disorders
Batten Disease (Batten-Spielmeyer-Vogt Disease)
Down Syndrome (Trisomy 21; Mongolism)
Down syndrome is the most common autosomal trisomy.
  • Karyotyping shows 47 chromosomes with trisomy 21 in most patients; caused by translocation, usually to chromosome 14 or to other D group chromosome in <5% of cases. Two percent of patients have mosaicism, with one cell population trisomic.
Leukocytes show decreased incidence of drumsticks (see Chapter 4) and mean lobe counts.
Increased leukocyte alkaline phosphatase staining reaction.
Serum acid phosphatase may be decreased.
Risk of developing acute lymphocytic or nonlymphocytic leukemia is increased. Incidence is 10 to 20× greater than in the general population.
Congenital acute myelogenous leukemia may occur within several months of birth; it is always fatal.
Transient leukemoid reaction (WBC count ≤400,000/μL) with many blasts without anemia, thrombocytopenia, or neutropenia; becomes normal within 3 months. Occurs only with trisomy 21; differentiated from congenital leukemia by bone marrow biopsy, including cytogenetic and immunohistochemical studies. Twenty-five percent or fewer of these Down syndrome infants develop acute leukemia within 3 years.
Increased susceptibility to infection (e.g., hepatitis).
Table 12-16. Chromosome Number and Karyotype in Various Clinical Conditions
  Chromosome Number and Karyotype Incidence
Normal male 46 XY  
Normal female 46 XX  
Suspected autosomal syndromes  
Down syndrome (mongolism; trisomy 21) 47 XX, G+, or 47 XY, G+ 1 in 700 live births (2% are 46 count due to translocation and have 10% risk of Down syndrome in subsequent pregnancies; 2% are 46/47 mosaics)
Trisomy D 1 47 XX, D+, or 47 XY, D+ 1 in 5,000 live births
  Translocations Rare
  Mosaics Rare
Trisomy E 18 47 XX, E+, or 47 XY, E+ 1 in 3,000 live births
  Translocations Rare
  Mosaics Rare
Trisomy D 13  
Trisomy 8, 9, 4p, 9p   Rare
Cri du chat syndrome 46 with partial B deletion 1 in 30,000 births
Others (e.g., 4p-, 5p-, 9p-, 13q-)  
Suspected sex chromosome syndromes  
Klinefelter’s syndrome 47 XXY 1 in 600 live male births
  48 XXXY Rare
  48 XXYY Rare
  49 XXXXY Rare
  49 XXXYY Rare
  Mosaics Infrequent
Turner’s syndrome 45 XO 1 in 3,000 live female births
  46 XX Rare
  Mosaics Infrequent
“Superfemale” 47 XXX 1 in 1,000–2,000 live female births
  48 XXXX Rare
  49 XXXXX Rare
  Mosaics Rare
“Supermale” 47 XXY 1 in 1,000 live male births
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Laboratory findings due to associated congenital abnormalities (e.g., GI, GU, cardiovascular systems).
Prenatal Screening and Diagnosis19,20
Optimum first-trimester screening (10–13 weeks) combines maternal age >35 years with 2 analytes: Free β-hCG (increased average of ≤2×) and pregnancy-associated plasma protein A (PAPP-A) (decreased average of 2.5×) combined with ultrasound nuchal translucency thickness. Detects ∼85% of cases, with 5% false-positive rate. There should be a 2- to 6-week interval between first and second screenings.
Optimum second-trimester screening (at 15–22 weeks) combines maternal age >35 years with four analytes in maternal serum: β-hCG (increased average of 2×), AFP, unconjugated estriol levels (decreased average of 30%), and inhibin A (increased average of 2×). Detects ≤80% of cases, with 5% false-positive rate, using ultrasound to date fetal age.
Ultrasound may also detect major malformations associated with fetal Down syndrome (e.g., nonimmune hydrops, thickened nuchal fold, cystic hygroma, especially absent nasal bone).
Combination of first- and second-trimester screenings detects ∼90% of cases, with <2% false-positive rate. In first trimester, nuchal translucency thickness and serum PAPP-A; wait for second-trimester tests; in second trimester AFP, hCG, urine estriol are performed.
  Normal Average Change Average Value Change in Down Syndrome Average Value Change in Trisomy 18
Maternal serum AFPa 15%/week during second trimester. 25%–30% lower 40% lower
Unconjugated estriola 25%/week 25%–30% lower 60% lower
hCGa   2× higher 70% lower
Maternal serum Inhibin Aa   2× higher  
PAPP-Ab 50%/week 2.5× lower Lower
Free β-hCGb Increased Increased Lower
Nuchal translucency thicknessb (typically 0.5–1.5 mm) 20%/week 2× higher Higher
PAPP-A, pregnancy-associated plasma protein A; β-HcG, β-human chorionic gonadotropin.
aOptimum time for screening = 15 to 22 weeks.
bOptimum time for screening = 10 to 13 weeks.
Use of Inhibin is moot. Ultrasound nuchal translucency thickness interpretation requires special training.
Footnote
19
Canick JA, Saller DN Jr, Lambert-Messerlian GM. Prenatal screening for Down syndrome. Current and future methods. Clin Lab Med 2003;23:395–411.
20
Wapner R, Thom E, Simpson JL, et al. First-trimester screening for trisomies 21 and 18. N Engl J Med 2003;349:1405–1413.
Maternal Serum AFP
AFP is a glycoprotein produced first by the yolk sac, then by the fetal liver. It reaches its maximum at 10 to 13 weeks of gestation, then declines to <100 μg/L by term. By age 2 years, reaches adult levels <5 μg/L.
Interpretation
  • Use of maternal serum AFP alone detects ≤25% of cases but should be combined (see previous). Ultrasound is used to verify gestational age, which has a profound effect on the calculated risk of Down syndrome.
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  • Decreased maternal blood level of AFP in pregnancy is a valuable screening test, but diagnosis should be confirmed by finding increased levels in amniotic fluid and sonography(to rule out missed abortion, molar pregnancy, absent pregnancy), and by chromosomal studies to confirm or refute the diagnosis. Average AFP is 25% to 30% lower in Down syndrome.
  • In midtrimester, usual range is 10 to 150 ng/mL; is usually reported as multiple of median (MoM) (normal 0.4–2.5 MoM) to minimize interlaboratory variability and adjust for patient’s race, gestational age, diabetes mellitus, twin pregnancy, and patient weight. MoM relates specific patient to entire screened population. 1.0 MoM is central value of a normal pregnancy. 2.0 MoM = 2× central value; 0.5 MoM = half central value.
  • MoM = measured AFP (μg/L) ÷ median AFP for gestational age (μg/L) × adjustments (especially for gestational age and race).
Decreased In
Down syndrome (trisomy 21; average value is 2× higher) and trisomy 18
Long-standing death of fetus
Overestimation of gestational age (underestimation of age in amniotic fluid sample)
Choriocarcinoma, hydatidiform mole
Increased maternal weight (does not affect amniotic fluid concentration)
Pseudopregnancy, nonpregnancy
Various drugs (therefore no medications for at least 12 hours before test)
Other unknown factors
Women with diabetes mellitus have values 20% to 40% lower than nondiabetic women.
Increased In
(Should confirm by increase in amniotic fluid)
  • Multiple pregnancy (>4.5 MoM)
  • Gestational age (for which values must be adjusted)
  • Race (10%–15% higher in blacks) (for which values must be adjusted)
Open neural tube defects (e.g., open spina bifida, anencephaly, encephalocele, myelocele); 80% of severe cases will be detected by AFP; hydrocephaly and microcephaly
Ventral wall defects associated with exposed fetal membrane and blood vessel surfaces, e.g., omphalocele, gastroschisis
Hydrops fetalis
Intrauterine death
Fetal-maternal hemorrhage
Esophageal or duodenal atresia
Cystic hygroma
Renal disorders (e.g., polycystic kidneys, renal agenesis, urethral obstruction)
Aplasia cutis
Sacrococcygeal teratoma
Tetralogy of Fallot
Turner syndrome
Oligohydramnios
Maternal causes (e.g., neoplasm that produces AFP, hepatitis)
Placental causes (e.g., infarction, thrombosis, inflammation, cystic changes, very large placenta)
Very rare benign hereditary familial elevation of serum AFP
Maternal Serum Human Chorionic Gonadotropin
hCG appears in maternal serum soon after pregnancy and reaches a peak by 8 to 10 weeks of gestation, then decreases to nadir at 18 weeks and then remains constant to end of pregnancy.
Use
Best single marker for Down syndrome screening but usually done as part of a three- or four-test analyte screen. Average value is 2× higher in Down syndrome.
Diagnosis of early pregnancy (see Pregnancy Test)
Diagnosis and effectiveness of therapy of germ cell tumors (see Chapter 14)
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Maternal Serum Unconjugated Estriol
Estriol originates from fetal adrenal, liver, and placenta. It begins to appear by the seventh to the ninth week of gestation.
Decreased In
Average value is 25% to 30% lower in Down syndrome.
Low values at 35 to 36 weeks of gestation will identify one third or fewer of “light for dates” infants.
Interpretation
Level >12 ng/mL rules out postmaturity in cases of prolonged gestation if there are no other diseases (e.g., diabetes mellitus, isoimmunization).
≤0.6 MoM in 5% of unaffected pregnancies and 26% of Down syndrome.
Safe levels indicate fetal well-being.
Increasing serial values rule out prolonged pregnancy and postmaturity.
Constant normal values are consistent with 40 to 41 weeks of gestation.
Declining values are consistent with prolonged gestation.
Low or significantly falling values are seen in fetal distress and postmaturity.
Pregnancy-Associated Plasma Protein A
PAPP-A is a high-molecular-weight glycoprotein of uncertain function. Levels normally increase 50%/week during the first trimester.
≤2.5× lower in Down syndrome pregnancy in second trimester.
After 14 weeks, PAPP loses its effectiveness; similar in affected and unaffected pregnancies.
Chromosomal Analysis of Amniotic Fluid
Can detect ∼20% of cases.
Trisomy 18 (Edward Syndrome)
Trisomy 18 is the second most common autosomal trisomy. Occurrence is usually sporadic; due to nondisjunction; increased maternal age. Seventy percent of pregnancies miscarry. Ninety percent of newborns die in the first year.
  • Screening in second trimester: maternal age>35combined with decreased AFP (average 40%), hCG (average 70%), and unconjugated estriol (average 60%) in maternal serum detects ∼70% of cases, with 0.4% false-positive rate.
  • Screening in first trimester: maternal age>35, decreased PAPP-A and free β-hCG with ultrasound. Inhibin A use is moot.
Triple screen of AFP, total hCG, unconjugated estriol has reported detection rate of 60%, with <0.7% false positives.
  • Karyotyping shows 47 chromosomes, with trisomy 18 in most patients or mosaicism or translocations.
Laboratory findings due to congenital abnormalities (e.g., cardiovascular, GU, GI systems).
Trisomy 13 (D1 Trisomy; Patau Syndrome)21
Trisomy 13 is the third most common autosomal trisomy, usually caused by chromosomal nondisjunction (>75% of cases). It may also be caused by translocation (10% of cases; parental carrier) or mosaicism (5% of cases). Over 80% of patients die in the first month; the 6-month survival rate is 5%.)
  • In peripheral blood smears, ≤80% of polymorphonuclear leukocytes (neutrophils and eosinophils) show an increased number of anomalous nuclear projections (tags,
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    threads, drumsticks, clubs); the nuclear lobulation may appear abnormal (nucleus may look twisted without clear separation of individual lobes, coarse lumpy chromatin, etc.). Present in almost all complete trisomic cases. Nuclear coils of chromatin by electron microscopy.
Fetal hemoglobins may persist longer than normal (i.e., be increased); these include HbF, Bart, Gower 2.
  • Decreased AFP in maternal serum and amniotic fluid. Has no pattern of diagnostic markers for prenatal screening.
Laboratory findings due to multiple congenital abnormalities (including almost pathognomonic tetrad of narrow palpebral fissures, microphthalmos, cleft palate, parieto-occipital scalp defect, and polydactyly).
  • Karyotyping shows numeric abnormality in 80% of cases: 47 XX, +13 or 47 XY, +13. Mosaicism is rare.
Footnote
21
Baty BJ, Blackburn BL, Carey JC. Natural history of trisomy 18 and trisomy 13. I. Growth, physical assessment, medical histories, survival, and recurrence risk. Am J Med Genet. 1994;49: 175–188.
Dysautonomia, Familial (Riley-Day Syndrome)
Dysautonomia is an autosomal recessive disorder (localized to chromosome 9 at 9q31-q33) of autonomic dysfunction occurring in Ashkenazi Jews; patients show difficulty in swallowing, corneal ulcerations, insensitivity to pain, motor incoordination, excessive sweating, diminished gag reflex, lack of tongue papillae, progressive kyphoscoliosis, pulmonary infections, etc.
Urine vanillylmandelic acid (VMA) (3-methoxy-4-hydroxymandelic acid) may be low, and homovanillic acid is increased.
In asymptomatic carriers, urine VMA may be lower than in healthy adults.
Decreased plasma dopamine β-hydroxylase (converts dopamine to norepinephrine).
Fragile X Syndrome of Mental Retardation
Fragile X syndrome is the most common form of inherited mental retardation. It is caused by mutations that increase the size of a specific DNA fragment of the X chromosome (in Xq27.3).
  • Direct diagnosis by DNA analysis using Southern blotting and PCR. Can also be used for prenatal diagnosis and to detect asymptomatic carriers. Can distinguish between full mutation, in which 100% of males and about 50% of females will be mentally impaired, and permutation, in which only ∼3% will be impaired.
Lesch-Nyhan Syndrome
Lesch-Nyhan syndrome is an X-linked recessive trait of complete absence of hypoxanthine-guanine phosphoribosyl transferase (HGPRT) that catalyzes hypoxanthine and guanine to their nucleotides, causing an accumulation of purines. The syndrome appears in male children, with choreoathetosis, mental retardation, and tendency to self-mutilation, biting, and scratching.
  • Increased serum uric acid levels (9–12 mg/dL).
  • Hyperuricuria
    • 3 to 4 mg of uric acid/mg creatinine
    • 40 to 70 mg of uric acid/kg body weight
    • 600 to 1,000 mg/24 h in patients weighing ≥15 kg
    • Marked variation in purine diet causes very little change
    • Orange crystals or sand in infants’ diapers
  • Deficiency of HGPRT activity detected in cultured fibroblasts (<1.2% of normal), RBC hemolysates (0%) establishes the diagnosis; in amniotic cells allows diagnosis in utero. DNA probes allow prenatal diagnosis.
  • Heterozygotes can be detected by study of individual hair follicles.
  • Variants with partial deficiency of HGPRT show 0% to 50% of normal activity in RBC hemolysates and >1.2% in fibroblasts; accumulate purines but no orange sand in diapers; no abnormality of CNS or behavior.
Laboratory findings due to secondary gout (tophi after 10 years, crystalluria, hematuria, urinary calculi, urinary tract infection, gouty arthritis, response to colchicine); patients die of renal failure by age 10 years unless treated.
Table 12-17. Comparison of Some Periodic Fever Syndrome24
  Familial Mediterranean Fever Hyper-IgD Syndrome TNF-Receptor-Associated Periodic Syndrome
Ancestry Sephardic Jews, Arabs, Turks, Armenians Western European (60% are Dutch, French) Scottish, Irish; now reported in others
Usual age at onset <20 y <1 y <20 y
Usual duration of attack <2 d 4–6 d >14 d
Inheritance Autosomal recessive Autosomal recessive Autosomal dominant
Chromosome 16 short arm 12 long arm 12 short arm
Gene MEFV encodes protein pyrin or marenostrin; five mutations are most frequent Mevalonate kinase gene; V377I mutation in >80% of patients Type 1 TNF receptor gene
AA amyloidosis Nephropathy develops in ≤60% of patients Not reported In 25% of affected families
Laboratory findings Decreased C5a inhibitor in serosal fluids Increased serum IgD (>100 IU/mL); associated increased IgA in 80% of cases Soluble type 1 TNF receptor is usually <1 ng/mL and mevalonate kinase activity is 5%–15% of normal in serum
Clinical symptoms of abdominal pain, skin lesions, arthralgia  
Other findings Myalgia is uncommon Cervical lymphadenopathy, enlarged liver, spleen Variable; conjunctivitis, localized myalgia
TNF, tumor necrosis factor.
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Periodic Fever Syndromes22
The periodic fever syndromes are inherited disorders with limited periods of fever and serositis that recur for years in otherwise healthy persons; the fever is accompanied by an increase in acute inflammatory reactants (e.g., ESR, CRP, WBC, fibrinogen, A amyloid, etc.) and different fever patterns.
P.649

Footnote
22
Drenth JPH, van der Meer JWM. Hereditary periodic fever. N Engl J Med 2001;345:1748.
Mediterranean Fever, Familial (Familial Paroxysmal Peritonitis)23
Familial Mediterranean fever is an autosomal recessive disorder caused by a defect on chromosome 16; it results from a lack of a specific protease in serosal fluids with recurrent polyserositis (peritonitis 93%, arthritis 47%, pleuritis 31%) and fever (92%) and myalgia (39%) lasting ≤96 hours, predominantly in Sephardic Jews, Arabs, Turks, and Armenians.
  • AA amyloidosis nephropathy develops in ≤60% of patients (arrested by colchicine prophylaxis); is usually fatal. Is not related to frequency or severity of clinical attacks; also involves GI, liver, spleen, skin, other sites.
  • Genetic labs usually screen for five most common mutations, which cause >70% of deleterious alleles.
Footnote
23
Tunca M, Akar S, Onen F, Turkish FMV Study Group, et al. Familial Mediterranean fever (FMF) in Turkey. Medicine (Baltimore) 2005;84(1):1–11.
Hyper-IgD Syndrome
  • Increased IgD (>100 IU/mL on more than one occasion) is constant. Associated with increased IgA in 80% of cases.
Mevalonate kinase activity = 5% to 15% of normal; complete deficiency in <1% of patients, causing mevalonic aciduria.
Variant form is also recognized.
Tumor Necrosis Factor Receptor-Associated Periodic Syndrome
  • Serum level of soluble type 1 tumor necrosis factor receptor is low (usually <1 ng/mL; increased in renal insufficiency, e.g., amyloidosis).
  • DNA gene sequencing detects mutations.
Other Periodic Syndromes include familial cold urticaria, Muckle-Wells syndrome, and aphthous stomatitis.