Definition: Autosomal recessively inherited inborn error of metabolism of phenylalanine characterized by deficiency of phenylalanine hydroxylase [MIM*261600] caused by mutation in the phenylalanine hydroxylase gene (PAH) on 12q; occasionally, dihydropteridine reductase [MIM*261630], caused by mutation in the dihydropteridine reductase gene (DHPR) on 4p; rarely, dihydrobiopterin synthetase [MIM*261640], caused by mutation in the pyruvoyl tetrahydropterin synthase gene (PTS) on 11q; or even more rarely, deficiency of guanidine triphosphate cyclohydrolase 1 [MIM*233910]. The disorder is characterized by inadequate formation of l-tyrosine, elevation of serum l-phenylalanine, urinary excretion of phenylpyruvic acid and other derivatives, and accumulation of phenylalanine and its metabolites, which can produce brain damage resulting in severe mental retardation, often with seizures, other neurologic abnormalities such as retarded myelination and deficient melanin formation leading to hypopigmentation of the skin and eczema.
[phenyl + ketone + G. ouron, urine]
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