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)[1]. 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.
References
Online Mendelian Inheritance in Man (OMIM)[2] entry on phenylketonuria [3]
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