A 5-month-old boy is brought by his parent for follow up. He was diagnosed with hyperphenylalaninemia by newborn screening on day one of age. He was placed on a special phenylalanine-restricted diet with tyrosine supplementation. laboratory test results indicate that the infant has a normal serum phenylalanine level. Careful examination, however, reveals some neurological abnormalities, including axial hypotonia and microcephaly. Further workup is notable for elevated prolactin, and his physician suspects a cofactor deficiency. Which of the following enzymes is most likely deficient in this patient?

Question

A 5-month-old boy is brought by his parent for follow up. He was diagnosed with hyperphenylalaninemia by newborn screening on day one of age. He was placed on a special phenylalanine-restricted diet with tyrosine supplementation.  laboratory test results indicate that the infant has a normal serum phenylalanine level.  Careful examination, however, reveals some neurological abnormalities, including axial hypotonia and microcephaly.  Further workup is notable for elevated prolactin, and his physician suspects a cofactor deficiency.  Which of the following enzymes is most likely deficient in this patient?

Quizplus · Accepted Answer

Eductional Objective: Dihydrobiopterin reductase deficiency results in impaired tetrahydrobiopterin (BH₄) levels. BH₄ is an important cofactor for both phenylalanine hydroxylase and tyrosine hydroxylase. Although phenylalanine levels can be corrected with dietary restriction, downstream deficiencies of dopamine, norepinephrine, epinephrine, and serotonin lead to progressive neurologic deterioration

A 5-Month-Old Boy Is Brought by His Parent for Follow