Which amino acid must be supplemented in diets of patients with PKU?

Patients with phenylketonuria (PKU) have a deficiency in the enzyme phenylalanine hydroxylase, which is necessary for the conversion of phenylalanine to tyrosine. As a result, individuals with PKU cannot adequately synthesize tyrosine, making it conditionally essential in their diets.

When phenylalanine is not converted to tyrosine, it can accumulate to harmful levels, leading to severe neurological damage and cognitive impairment. Therefore, it is crucial for patients with PKU to restrict their intake of phenylalanine, which is found in many protein-rich foods, while supplementing their diet with tyrosine. This supplementation helps to ensure adequate production of important neurotransmitters and supports overall metabolic function despite the enzyme deficiency present in PKU.

This understanding highlights the necessity of including tyrosine in the diet of PKU patients, as it alleviates some of the metabolic consequences of their condition.