phenylketonuria

Autosomal recessively inherited inborn error of metabolism of phenylalanine characterized by deficiency of 1) phenylalanine hydroxylase [MIM*261600] caused by mutation in the phenylalanine hydroxylase gene (PAH) on 12q; 2) occasionally, dihydropteridine reductase [MIM*261630], caused by mutation in the dihydropteridine reductase gene (DHPR) on 4p; 3) rarely, dihydrobiopterin synthetase [MIM*261640], caused by mutation in the pyruvoyl tetrahydropterin synthase gene (PTS) on 11q; or 4) even more rarely, 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. Cf.:hyperphenylalaninemia. SYN: Folling disease, phenylpyruvate oligophrenia. [phenyl + ketone + G. ouron, urine]

- nonclassical p. SYN: malignant hyperphenylalaninemia.

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phe·nyl·ke·ton·uria .fen-əl-.kēt-ən-'(y)u̇r-ē-ə, .fēn- n a metabolic disorder that is caused by an enzyme deficiency resulting in the accumulation of phenylalanine and its metabolites (as phenylpyruvic acid) in the blood and their excess excretion in the urine, that is inherited as an autosomal recessive trait, and that causes usu. severe mental retardation, seizures, eczema, and abnormal body odor unless phenylalanine is restricted from the diet beginning at birth abbr. PKU called also phenylpyruvic amentia, phenylpyruvic oligophrenia

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n.

an inherited defect of protein metabolism (see inborn error of metabolism) causing an excess of the amino acid phenylalanine in the blood, which damages the nervous system and leads to severe mental retardation. Screening of newborn infants by testing a blood sample for phenylalanine (see Guthrie test) enables the condition to be detected soon enough for dietary treatment to prevent any brain damage: the baby's diet contains proteins from which phenylalanine has been removed. The gene responsible for phenylketonuria is recessive, so that a child is affected only if both parents are carriers of the defective gene.

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phen·yl·ke·ton·uria (PKU) (PKU1) (fen″əl-ke″to-nuґre-ə) the most severe manifestation of hyperphenylalaninemia (q.v.) that is due to mutation in the PAH gene (locus: 12q24.1), which encodes phenylalanine hydroxylase, with virtual absence of enzyme activity and accumulation and excretion of phenylalanine, phenylpyruvic acid, and related compounds. It is an autosomal recessive trait characterized by severe mental retardation, tumors, seizures, hypopigmentation of hair and skin, eczema, and mousy odor, all preventable by early restriction of dietary phenylalanine. Called also classic p.