Phenylketonuria is caused by deficiency of which enzyme?

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Multiple Choice

Phenylketonuria is caused by deficiency of which enzyme?

Phenylketonuria results from a deficiency of phenylalanine hydroxylase, the liver enzyme that converts phenylalanine to tyrosine with the help of the cofactor tetrahydrobiopterin. When this enzyme is lacking or not functioning, phenylalanine accumulates in the blood and tissues while tyrosine becomes scarce, leading to neurotoxicity and developmental problems if not managed. This is why early detection and a phenylalanine-restricted diet are used to prevent intellectual disability. The other enzymes—tyrosine hydroxylase, tryptophan hydroxylase, and DOPA decarboxylase—are involved in other neurotransmitter pathways (catecholamines and serotonin) and do not cause classic PKU when deficient.

Phenylketonuria results from a deficiency of phenylalanine hydroxylase, the liver enzyme that converts phenylalanine to tyrosine with the help of the cofactor tetrahydrobiopterin. When this enzyme is lacking or not functioning, phenylalanine accumulates in the blood and tissues while tyrosine becomes scarce, leading to neurotoxicity and developmental problems if not managed. This is why early detection and a phenylalanine-restricted diet are used to prevent intellectual disability. The other enzymes—tyrosine hydroxylase, tryptophan hydroxylase, and DOPA decarboxylase—are involved in other neurotransmitter pathways (catecholamines and serotonin) and do not cause classic PKU when deficient.

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