What amino acid is found at increased levels in individuals with Phenylketonuria (PKU)?

In Phenylketonuria (PKU), individuals exhibit elevated levels of phenylalanine due to a deficiency in the enzyme phenylalanine hydroxylase. This enzyme is responsible for converting phenylalanine to tyrosine, which is an essential step in the metabolism of phenylalanine. When this enzymatic pathway is disrupted, phenylalanine accumulates in the body.

The clinical significance of elevated phenylalanine levels is critical because excessive accumulation can lead to neurotoxicity and cognitive deficits. Therefore, management of PKU focuses on reducing phenylalanine intake through dietary restrictions to prevent these complications.

While tyrosine can also be of clinical interest due to its connection to the pathway, it is seen at decreased levels in PKU because it is not effectively synthesized due to the lack of phenylalanine conversion. Hence, the correct answer emphasizes the accumulation of phenylalanine as the hallmark of this metabolic disorder.