Phenylketonuria (PKU) is an inborn error in the metabolism of phenyl-alanine, which leads to idiocy in early childhood. About 25 % of all PKU patients suffer from epileptic seizures and minor neurological symptoms such as tremors, ataxia, and hypertonicity of muscles. The basic biochemical defect is lack of the hydroxylating enzyme responsible for the conversion of phenylalanine to tyrosine in the liver. As a result, a high plasma concentration of phenylalanine occurs along with several abnormal metabolites; these are excreted by PKU patients as phenylpyruvic acid, a deaminated product of excess phenylalanine in plasma. A correlation between PKU and abnormal indole metabolism is also evident. This is characterized by a decrease in 5-hydroxyindoleacetic acid urinary levels and by an increased urinary excretion of indole-3-acetic acid. Hsia et al. (1964) have suggested three possibilities to explain PKU: (1) excessive phenylalanine might inhibit the hydroxylation of tryptophan metabolism in brain or liver, thus reducing available 5-HTP; (2) this excess might also inhibit the active transport of tryptophan or 5-HTP across the blood-brain barrier or brain cell membrane; and (3) excess phenylalanine and its metabolites might inhibit the decarboxylation of 5-HTP.
KeywordsMedial Forebrain Bundle Brain Serotonin Dopa Decarboxylase Xanthurenic Acid Histochemical Fluorescence
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