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Download THE NORMAL METABOLISM OF PHENYLALANINE (pathways a
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PHENYLKETONURIA (PKU) FACT SHEET THE NORMAL METABOLISM OF PHENYLALANINE (pathways a and b) AND THE ABNORMAL METABOLISM IN PHENYLKETONURIC SUBJECTS (pathway c) HYDROXYPHENYLACETIC ACID Dietry sources, particularly plant proteins BREAKDOWN (c) PHENYLALANINE HYDROXYLASE PHENYLALANINE* (a) TYROSINE (c) (b) PHENYLACETIC ACID* BODY PROTEINS *Agents, thought to be responsible for mental retardation, which accumulate in phenylketonuric subjects (PKU). These are broken down into ketone bodies which appear in the urine. Other symptoms include skin lesions. Test Ferric chloride + urine of new born baby Green colour in the presence of ketone bodies. Treatment A strictly controlled phenylalanine low diet must be followed for life. No protein rich foods (e.g. meat, eggs, pulses). No aspartame sweetner. As phenylalanine is itself an essential amino acid small doses must be supplied. Other nutrients may need supplementing. Frequency 1 in 10 000 in Caucasians of NW Europe Causes 1. A single mutant recessive allele of the Phenylalanine Hydroxylase (PAH) gene. This results in the inability to produce the enzyme. Locus: Long arm of Chromosome 12. 2. Dietary excess of plant proteins which results in the exhaustion of a protein cofactor (pterin) needed by the enzyme. Evolution Heterozygotes (carriers) are thought to be less susceptible to toxins produced by the moulds Aspergillus and Penecillium. These grow on foods in damp wet climates (e.g. NW Europe). Heterozygous women show lower spontaneous abortion rates. 14/05/2017