This family contains the paired amphipathic helix (PAH) repeat.
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Phenylketonuria (PKU) is a rare metabolic disorder caused by a deficiency in the production of the hepatic (liver) enzyme phenylalanine hydroxylase (PAH).
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This is the only role of PAH in the body.
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Mutations in the PAH gene prevent the liver from producing adequate levels of the PAH enzyme needed to break down phenylalanine.
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The PAH gene and its PKU mutations are found on chromosome 12 in the human genome.
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In more detail, PKU mutations can involve many different types of changes, such as deletions and insertions, in the DNA of the gene that codes for the PAH enzyme.
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The normal PAH gene is dominant to recessive PKU mutations.
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A carrier does not display any symptoms of the disease because the carrier's liver produces normal quantities of the PAH enzyme.
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Subsequent diagnostic procedures (called mutation analysis and genotype determination) can actually identify the specific types of PAH gene mutations inherited by PKU infants.