A medical genetics team is evaluating several pediatric patients with suspected inborn errors of amino acid metabolism. Based on the findings provided, match each patient's clinical presentation with the specific enzyme defect most likely responsible for their condition.
- An infant presenting with fair pigmentation, severe eczematous rash, and a distinct musty body odor.Phenylalanine hydroxylase
- A young child evaluated for a marfanoid habitus, downward lens subluxation, and an unprovoked deep vein thrombosis.Cystathionine beta-synthase
- A school-aged child noted to have dark connective tissue pigmentation and urine that turns black when exposed to ambient air for prolonged periods.Homogentisate oxidase
- A neonate exhibiting severe lethargy, fluctuating muscle tone, and a characteristic sweet, burnt-sugar urinary scent.Branched-chain alpha-ketoacid dehydrogenase
Answer
The clinical presentations match with their respective enzyme deficiencies as follows: the infant with eczema and musty odor has phenylketonuria (phenylalanine hydroxylase defect); the child with marfanoid features and thrombosis has homocystinuria (cystathionine beta-synthase defect); the child with dark urine has alkaptonuria (homogentisate oxidase defect); and the neonate with sweet-smelling urine has maple syrup urine disease (branched-chain alpha-ketoacid dehydrogenase defect).
Each enzyme defect results in the accumulation of specific upstream metabolites and a deficiency of downstream products, producing distinct clinical syndromes. Phenylalanine hydroxylase deficiency causes PKU; cystathionine beta-synthase deficiency causes homocystinuria; homogentisate oxidase deficiency causes alkaptonuria; and branched-chain alpha-ketoacid dehydrogenase deficiency causes MSUD.
Step-by-Step Solution
Key Concept
Clinical recognition of amino acid metabolism disorders