| Branched-chain amino aciduria (maple syrup urine disease) | Defective branched-chain amino acid breakdown (Fig. 44-1) | Coma, convulsions, vomiting, respiratory failure in neonate |
| Branched-chain organic acidurias | Failure of organic acid oxidation (Fig. 44-1), isovaleric, methylmalonic, propionic, etc. | Similar to above, may be metabolic acidemia and odd odor; often confused with sepsis of newborn; urine contains excessive amounts of different organic acids, depending on the nature of the defect; partial defects may present in later infancy or childhood |
| Glutaric acidurias | Type I: Primary defect of glutarate oxidation (Fig. 44-3) | Severe basal ganglia/cerebellar disease with macrocephaly, onset 1 to 2 years |
| Type II: Defect of electron transfer flavoprotein (Fig. 44-3) | Fulminant neurological syndrome of the neonate, often with renal/hepatic cysts, usually fatal |
| Phenylketonuria (PKU) | Usually defect of phenylalanine hydroxylase. In rare cases, defect of biopterin metabolism (Fig. 44-4, reaction 1) | Normal at birth, mental retardation in untreated children, avoidable with early institution of diet therapy, prognosis less favorable in PKU secondary to defect of biopterin metabolism |
| Nonketotic hyperglycinemia | Defect of glycine-cleavage system (Fig. 44-5) | Intractable seizures in neonate, usually fatal in first few weeks of life |
| Homocystinuria | Usually a failure of cystathionine synthase (Fig. 44-2, reaction 5), rarely associated with aberrant vitamin B12 metabolism (Fig. 44-2) | Thromboembolic diathesis, marfanoid habitus, ectopia lentis; mental retardation is frequent |
| Urea cycle defects | Failure to convert ammonia to urea via urea cycle (Fig. 44-6) | Coma, convulsions, vomiting, respiratory failure in neonate; often mistaken for sepsis of the newborn; mental retardation, failure to thrive, lethargy, ataxia and coma in the older child; associated with hyperammonemia and abnormalities of blood aminogram |
| Defects of biotin metabolism | Failure to “activate” biotin, which is important in carboxylation of organic acids | Hypotonia, ataxia, acidosis, coma, dermatitis in the neonate; mental retardation and deafness in the older child |
| Disorders of glutathione metabolism | Defective synthesis of glutathione, the major intracellular antioxidant (Fig. 44-7) | Spinocerebellar degeneration, mental retardation, cataracts, hemolysis; severe acidosis in some cases |
| Disorders of GABAmetabolism | Often an absence of succinic semialdehyde dehydrogenase | Hypotonia, ataxia, mental retardation in the older child; increased urine 4-OH-butyric acid |
| Canavan's disease | Absence of N-acetylaspartate acylase | Rapidly progressive demyelinating disease of infancy |
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