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Biochemistry, cell biology, and genetics

Phenylalanine, tyrosine, and branched-chain disorders

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SAMPLE QUESTION

A 19-month-old boy who did not undergo newborn screening is evaluated for developmental delay and seizures. He has eczema, a musty body odor, and lighter hair than his siblings. Plasma phenylalanine is markedly elevated. A metabolic dietitian begins a phenylalanine-restricted feeding plan.

Which amino acid must now be supplied in the diet because its endogenous production is impaired by this disorder?