A child presents with intellectual disability, fair hair, blue eyes, and eczema. Urine analysis reveals elevated phenylalanine levels and a deficiency in tetrahydrobiopterin reductase. What enzyme is primarily affected in this patient?

Question

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C) Dihydropteridine reductase. Dihydropteridine reductase (DHPR) regenerates tetrahydrobiopterin (BH4). BH4 is a cofactor for phenylalanine hydroxylase. A deficiency in DHPR leads to secondary phenylalanine hydroxylase dysfunction, causing hyperphenylalaninemia and associated symptoms.

A child presents with intellectual disability, fair hair, blue eyes, and eczema. Urine analysis reveals elevated phenylalanine levels and a deficiency in tetrahydrobiopterin reductase. What enzyme is primarily affected in this patient?

✓ Correct Answer: Option C

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