What does Phenylketonuria (PKU) lack a specific enzyme to process?

Phenylketonuria (PKU) is a genetic disorder characterized by the individual's inability to metabolize phenylalanine, an amino acid found in many protein-containing foods. In individuals with PKU, there is a deficiency of the enzyme phenylalanine hydroxylase, which is essential for converting phenylalanine into tyrosine, an important amino acid that contributes to the production of neurotransmitters and other critical compounds in the body.

Without this enzyme, phenylalanine accumulates to toxic levels in the body, leading to serious neurological issues and developmental delays if not managed through strict dietary control. Therefore, the correct answer highlights the specific dietary component that individuals with PKU must limit or avoid entirely to prevent health complications.

In contrast, while proteins are a source of phenylalanine, the focus on the specific compound the body cannot process makes dietary phenylalanine the accurate choice. Sugars and carbohydrates are not directly related to the metabolic defect of PKU and do not pose the same risks as excess phenylalanine in an individual's diet.