A 3-year-old boy who recently immigrated to the United States is brought to the physician by his parents because he has not yet begun to walk or speak. Assessment of his developmental milestones shows severe intellectual disability. He dies 6 months later from refractory seizures resulting in respiratory failure. Autopsy shows pallor of the substantia nigra, locus ceruleus, and vagal nucleus dorsalis. The underlying condition responsible for this patient's death is most likely caused by a deficiency of which of the following enzymes?

Question

A 3-year-old boy who recently immigrated to the United States is brought to the physician by his parents because he has not yet begun to walk or speak.  Assessment of his developmental milestones shows severe intellectual disability.  He dies 6 months later from refractory seizures resulting in respiratory failure.  Autopsy shows pallor of the substantia nigra, locus ceruleus, and vagal nucleus dorsalis.  The underlying condition responsible for this patient's death is most likely caused by a deficiency of which of the following enzymes?

Quizplus · Accepted Answer

Eductional Objective: Deficiency of the enzyme phenylalanine hydroxylase or its cofactor tetrahydrobiopterin causes accumulation of phenylalanine in body fluids and the central nervous system.  Homozygous infants are normal at birth but gradually develop severe intellectual disability and seizures if left untreated.  Hypopigmentation of the skin, hair, eyes, and catecholaminergic brain nuclei is also frequently seen.

A 3-Year-Old Boy Who Recently Immigrated to the United States