Hyperphenylalanemia
Encyclopedia
Hyperphenylalaninemia is a medical condition characterized by mildly or strongly elevated levels of the amino acid
phenylalanine
in the blood. Severe hyperphenylalaninemia results in phenylketonuria
(PKU)http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=261600. Phenylalanine concentrations ([phe]) are routinely screened in newborns by the Guthrie test
, which takes a few drops of blood from the heel of the infant. Standard [phe] concentrations in unaffected persons are ~60 uM: [phe] concentrations in persons with untreated phenylketonuria may be times 600 ~ 2400 uM, which indicate that the child is at risk for severe mental retardation
. Phenylketonuria is classed as an autosomal recessive condition: in heterozygotes from, [phe] shows a moderate elevation, perhaps two-fold over unaffected homozygotes, which is classified as Hyperphenylalaninemia [hyper + phenylalanine + emia = high phe in blood].
Persons with the genotype for PKU are unaffected in utero because maternal circulation prevents buildup of [phe]. After birth, PKU in newborns is treated by a special diet with highly restricted phenylalanine content. Persons with genetic predisposition to PKU have normal mental development on this diet. Previously, it was thought safe to withdraw from the diet in the late teens or early twenties, after the central nervous system
was fully developed; recent studies suggest some degree of relapse and a phenylalanine-restricted diet is now recommended.
PKU or Hyperphenylalaninemia may also occur in persons without the PKU genotype. If the mother has the PKU genotype but has been treated so as to be asymptomatic, high levels of [phe] in the maternal blood circulation may affect the non-PKU fetus during gestation. Mothers successfully treated for PKU are advised to return to the [phe]-restricted diet during pregnancy.
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
phenylalanine
Phenylalanine
Phenylalanine is an α-amino acid with the formula C6H5CH2CHCOOH. This essential amino acid is classified as nonpolar because of the hydrophobic nature of the benzyl side chain. L-Phenylalanine is an electrically neutral amino acid, one of the twenty common amino acids used to biochemically form...
in the blood. Severe hyperphenylalaninemia results in phenylketonuria
Phenylketonuria
Phenylketonuria is an autosomal recessive metabolic genetic disorder characterized by a mutation in the gene for the hepatic enzyme phenylalanine hydroxylase , rendering it nonfunctional. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine...
(PKU)http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=261600. Phenylalanine concentrations ([phe]) are routinely screened in newborns by the Guthrie test
Guthrie test
The Guthrie test, also known as the Guthrie bacterial inhibition assay, is a medical test performed on newborn infants to detect phenylketonuria, an inborn error of amino acid metabolism. The test has been widely used throughout North America and Europe as one of the core newborn screening tests...
, which takes a few drops of blood from the heel of the infant. Standard [phe] concentrations in unaffected persons are ~60 uM: [phe] concentrations in persons with untreated phenylketonuria may be times 600 ~ 2400 uM, which indicate that the child is at risk for severe mental retardation
Mental retardation
Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...
. Phenylketonuria is classed as an autosomal recessive condition: in heterozygotes from, [phe] shows a moderate elevation, perhaps two-fold over unaffected homozygotes, which is classified as Hyperphenylalaninemia [hyper + phenylalanine + emia = high phe in blood].
Persons with the genotype for PKU are unaffected in utero because maternal circulation prevents buildup of [phe]. After birth, PKU in newborns is treated by a special diet with highly restricted phenylalanine content. Persons with genetic predisposition to PKU have normal mental development on this diet. Previously, it was thought safe to withdraw from the diet in the late teens or early twenties, after the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
was fully developed; recent studies suggest some degree of relapse and a phenylalanine-restricted diet is now recommended.
PKU or Hyperphenylalaninemia may also occur in persons without the PKU genotype. If the mother has the PKU genotype but has been treated so as to be asymptomatic, high levels of [phe] in the maternal blood circulation may affect the non-PKU fetus during gestation. Mothers successfully treated for PKU are advised to return to the [phe]-restricted diet during pregnancy.