In which metabolic disorder is there a defect in the breakdown of phenylalanine?

Phenylketonuria, commonly referred to as PKU, is a metabolic disorder characterized by a defect in the enzyme phenylalanine hydroxylase, which is responsible for the conversion of phenylalanine to tyrosine. When this enzyme is deficient or absent due to a genetic mutation, phenylalanine accumulates in the body, leading to a range of neurological and developmental issues if not managed appropriately through dietary restrictions.

The significance of recognizing PKU lies in its implications for diet and health. Individuals with this disorder must adhere to a low-phenylalanine diet, particularly during infancy and childhood, to prevent intellectual disability and other severe health problems. If PKU is diagnosed early through newborn screening, treatment can effectively minimize the impacts of the disorder, highlighting the importance of understanding this condition.

Other conditions mentioned have different metabolic pathways or enzyme deficiencies unrelated to phenylalanine metabolism. Conditions like maple syrup urine disease involve the breakdown of branched-chain amino acids, while tyrosinemia pertains to the metabolism of tyrosine and its precursors. Cystathioninuria, in contrast, involves an issue with the metabolism of cysteine and does not relate to phenylalanine. Hence, the clear connection of