Question
A 4-year-old boy of a first-degree consanguineous couple was noted by the parents to have darkening of the urine to an almost black color when it was left standing. He has a normal sibling, and there are no other medical problems. Growth and development to date are normal. Which of the following is most likely to be elevated in this patient?
A. Methylmalonate
B. Homogentisate
C. Phenylpyruvate
D. αlpha-ketoisovalerate
Show Answer
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Correct Answer » B
Explanation
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* Alkaptonuria is a rare metabolic disease involving a deficiency in homogentisic acid oxidase, and the subsequent accumulation of homogentisic acid in the urine, which turns dark upon standing.
* The elevation of
→ methylmalonate (due to methylmalonyl CoA mutase deficiency),
→ Phenylpyruvate (due to phenylalanine hydroxylase deficiency),
→ α-ketoisovalerate (due to branched-chain α-keto acid dehydrogenase deficiency),
→ Homocysteine (due to cystathionine β-synthase deficiency)
* All of these are inconsistent with a healthy child with a darkening of the urine.
