What condition is caused by an inability to convert phenylalanine to tyrosine?

Phenylketonuria (PKU) is a genetic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine to tyrosine. When this enzyme is deficient or absent, phenylalanine accumulates in the body, leading to a range of neurological issues and developmental delays if not managed properly through dietary restrictions.

The clinical manifestations of PKU typically include intellectual disability, seizures, and behavioral problems if high levels of phenylalanine are present during early development. A special low-phenylalanine diet initiated early in life can help prevent these complications, highlighting the importance of early diagnosis through newborn screening programs.

Other disorders mentioned in the choices relate to different metabolic pathways or conditions. For example, alkaptonuria is linked to a deficiency in the enzyme that breaks down homogentisic acid, cystic fibrosis affects the movement of chloride ions across cell membranes, and maple syrup urine disease involves a defect in the branched-chain alpha-keto acid dehydrogenase complex, which is entirely distinct from the phenylalanine-tyrosine conversion pathway. Therefore, the key connection to PKU is the inability to convert phenylalanine into tyrosine