Amino Acid & Protein Metabolism · NEET PG Preparation Biochemistry
A 6-year-old boy is brought to the clinic for evaluation of tall stature, long slender fingers (arachnodactyly), downward lens dislocation (ectopia l…
Practice question from Amino Acid & Protein Metabolism (NEET PG Preparation Biochemistry), with the correct answer and a step-by-step solution.
medium · MCQ · Q-E59F0F
A 6-year-old boy is brought to the clinic for evaluation of tall stature, long slender fingers (arachnodactyly), downward lens dislocation (ectopia lentis), and a history of thromboembolic events. Laboratory tests show elevated plasma homocysteine and methionine levels. This condition is most commonly due to a defect in which of the following enzymes?
- A.Methionine synthase
- B.Cystathionine beta-synthaseCorrect answer
- C.Methylmalonyl-CoA mutase
- D.Cystathionase
Solution
Classical homocystinuria is caused by a deficiency of cystathionine beta-synthase, which converts homocysteine to cystathionine. Clinical features include marfanoid habitus, ectopia lentis (typically downward, unlike Marfan syndrome which is upward), intellectual disability, and a high risk for thromboembolism.
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