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.

See Figures 12-1 and 12-2 and Table 12-5.

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	HCO₃^- (mEq/ L)
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.

See Table 12-6.

(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

See Table 12-3.

(5) Mixed Acid-Base Disturbances

Mixed acid-base disturbances must always be interpreted with clinical data and other laboratory findings.

See Table 12-7.

(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

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

See Chapter 11 and Table 11-13.

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

See Chapter 11.

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

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 Table 12-8 and Figure 12-4.

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

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.

⁷http://www.cdc.gov/nceh/dls/newborn_screening.htm; http://www.savebabies.org.

⁸http://www.ncbi.nlm.nih.gov/omim/.

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 metabolism^a
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

See Chapter 5.

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		Combined hyperlipidemia (mixed hyperlipidemia)			Combined fat- and carbohydrate-induced hypergly-ceridemia
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
Chylomicron^a	Marked I	0	0	0	0
Beta-lipoprotein^b	N or D	I	I	I, floating beta	N or I	I
Pre–beta-lipoprotein^c	N or D	N	I	I	I
Alpha-lipoprotein^d
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

See Figure 12-5.

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

See Tables 12-10 and 12-11.

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.

See Table 12-10.

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

¹¹http://www.msud-support.org.

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)

(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)

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	12q25.2–q25.3	20	Lysosomal α-glucosidase
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	1p21	20	Amylo-1,6-glucosidase (debrancher enzyme)		Infancy	↓↓Glucose
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	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
V	11q13	5	Muscle phosphorylase	Moderate accumulation of normal structure MM		Cramps on exercise → no ↑blood lactate; myoglobinuria
McArdle syndrome	11q13	5	Muscle phosphorylase	Moderate accumulation of normal structure MM		Cramps on exercise → no ↑blood lactate; myoglobinuria
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	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^-
MM, skeletal muscle; CNS, central nervous system; cAMP, cyclic adenosine monophosphate; ↔, variable; ↓ to ↓↓↓↓, degree of decrease.

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P.619

P.620

P.621

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.

See Figures 12-7 and 12-8 and Table 12-13.

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, Location^a	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
	Chief Site of Porphyrin Over-production	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; ↑ALA^b, ↑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 negative^a ↑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	Precipitated by	Comment
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

See Table 12-15.

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

See Table 12-16. See Chapter 13.

Batten Disease (Batten-Spielmeyer-Vogt Disease)

See Chapter 11, Table 11-20.

Down Syndrome (Trisomy 21; Mongolism)

Down syndrome is the most common autosomal trisomy.

See Table 12-16.

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

See Table 12-8 and Figure 12-4.

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 AFP^a	15%/week during second trimester.	25%–30% lower	40% lower
Unconjugated estriol^a	25%/week	25%–30% lower	60% lower
hCG^a		2× higher	70% lower
Maternal serum Inhibin A^a		2× higher
PAPP-A^b	50%/week	2.5× lower	Lower
Free β-hCG^b	Increased	Increased	Lower
Nuchal translucency thickness^b (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.

See “Obstetric Monitoring of the Fetus and Newborn,” Chapter 14.

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.

See Chapter 4.

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%.)

See Table 12-8.

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

See Table 12-17.

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.

	Interpretation of Diagnostic Tests 8th Edition
	© 2007 Lippincott Williams & Wilkins

Interpretation of Diagnostic Tests8th Edition

Interpretation of Diagnostic Tests
8th Edition