phenylketonuria (PKU) /fen′əlkē′tōnyo͝or″ē·ə, fē′nəl-/ , abnormal presence of phenylketone and other metabolites of phenylalanine in the urine, characteristic of an inborn metabolic disorder caused by the absence or a deficiency of phenylalanine hydroxylase, the enzyme responsible for the conversion of the amino acid phenylalanine into tyrosine. Accumulation of phenylalanine is toxic to brain tissue. Untreated individuals have very fair hair, eczema, a mousy odor of the urine and skin, and progressive cognitive impairment. Treatment consists of a diet low in phenylalanine. Phenylketonuria occurs approximately once in 16,000 births in the United States. Most states require a screening test for all newborns. See also Guthrie’s bacterial inhibition assay. −phenylketonuric, adj.
