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. α-Ketoisovalerate

Answer 1

The Correct Option is B

The scenario described is characteristic of a condition known as Alkaptonuria, an autosomal recessive disorder due to a deficiency in the enzyme homogentisate 1,2-dioxygenase. This enzyme is crucial in the metabolic pathway of breaking down tyrosine. The deficiency leads to an accumulation of homogentisate, which darkens on exposure to air, causing the urine to turn black upon standing. This phenomenon is known as urine ochronosis.

Given the information:

• Darkening of the urine: A result of the oxidation of homogentisate to a melanin-like polymer.
• Consanguineous relationship: Increases the likelihood of autosomal recessive disorders like Alkaptonuria.
• Normal sibling: An unaffected carrier or completely non-carrier is possible because Alkaptonuria is recessive.

Thus, the most likely elevated compound in this patient is homogentisate, confirming the diagnosis of Alkaptonuria.