Question
A 38-year-old male is being evaluated for a long history of pain and stiffness in both shoulders and both knees. Physical examination shows brown spots on his sclerae and diffuse darkening of the helix of his ears. Which of the following enzymes is most likely deficient in this patient:
| A. |
Phenylalanine hydroxylase
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| B. |
Dopamine hydroxylase
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| C. |
Tyrosinase
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| D. |
Homogentisic acid oxidase
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Show Answer
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Correct Answer � D
Explanation
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Ans. D.Homogentisic acid oxidase
Alkaptonuria is a relatively benign childhood disorder that matures to arthritis in adult life. Alkaptonuria is an autosomal-recessive disorder caused by a deficiency of the enzyme homogentisic acid oxidase, which normally metabolizes homogentisic acid into maleylacetoacetate. Accumulated homogentisic acid causes pigment deposits in connective tissues throughout the body. During adulthood, these deposits become apparent in the sclera and ear cartilage. Deposits also occur in large joints and the spine, causing ankylosis and motion restriction. A distinctive characteristic of alkaptonuria is that the urine of affected patients turns black when exposed to room air. This color change occurs as homogentisic acid is oxidized .
