Dictionary of Human Evolution and Biology

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Abbreviation for phenylketonuria, a heritable autosomal recessive condition characterized by an inability to metabolize dietary phenylalanine; the subsequent toxic accumulation of this amino acid can cause mental defects. Symptoms begin to appear at about 4 months of age, and include irritability, depigmented and dry skin with a musty odor, and abnormal EEG patterns with seizures; phenotypic symptoms are variable. There are five types; in classic or type I PKU the defective enzyme is hepatic phenylalanine hydroxylase, PAH, which results in failure to convert phenylalanine to tyrosine; this causes abnormal myelin formation. PKU can be managed by a phenylalanine-deficient diet but early detection is difficult; after six months the neuronal damage is irreparable. Recent mass screenings for carriers and dietary management of PKU has resulted in longer lives for many PKU-affected babies; one consequence was an overall increase in the frequency of the abnormal allele, as well as a clinically new condition known as maternal PKU (see below). Aka Følling disease.

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