Inborn Errors of Metabolism · NEET PG Preparation Biochemistry
An 8-year-old boy is evaluated for joint pain, particularly in the lower back and large joints. Physical examination reveals a bluish-black discolora…
Practice question from Inborn Errors of Metabolism (NEET PG Preparation Biochemistry), with the correct answer and a step-by-step solution.
medium · MCQ · Q-36351F
An 8-year-old boy is evaluated for joint pain, particularly in the lower back and large joints. Physical examination reveals a bluish-black discoloration of the sclerae and ear cartilage (ochronosis). His urine turns dark upon standing and exposure to air. A defect in which of the following enzymes is responsible for this condition?
- A.Phenylalanine hydroxylase
- B.Homogentisate 1,2-dioxygenaseCorrect answer
- C.Tyrosinase
- D.Fumarylacetoacetate hydrolase
Solution
Alkaptonuria is a rare autosomal recessive disorder caused by a deficiency of homogentisate 1,2-dioxygenase, an enzyme in the tyrosine degradation pathway. This causes accumulation of homogentisic acid, which polymerizes into dark pigments deposited in connective tissues (ochronosis) and darkens upon urine alkalinization/oxidation.
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