Conversion of Phenylalanine to Phenethylamine in Patients with Phenylketonuria

Summary 1. An increased production of phenethylamine was found in patients with phenylketonuria. 2. Phenethylamine synthesis was markedly reduced by α-methyldopa, an inhibitor of aromatic l-amino acid decarboxylase. This suggests that the synthesis of phenethylamine from phenylalanine in humans is catalyzed by this decarboxylase. 3. Since aromatic l-amino acid decarboxylase is present in brain, it is likely that increased amounts of phenethylamine are synthesized in the central nervous system of patients with phenylketonuria.