Phenylketonuria (PKU; OMIM#261600) is an inherited metabolic disease where a genetic error results in a partial or complete de-activation of the enzyme phenylalanine hydroxylase (PAH) which normally metabolizes the amino acid phenylalanine (Phe; E.C. 1.14.16.1) into tyrosine (a precursor of dopamine). The gene discussed is PAH; the disease is phenylketonuria.