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1. Metabolism of the Branched Chain Organic Acids

Catabolism of the essential branched chain amino acids, leucine, isoleucine, and valine begins with transamination to their 2-oxo branched chain organic acids, then oxidative decarboxylation to form branched chain acyl coenzyme A (CoA) products. The branched chain amino acid and organic acid disorder maple syrup urine disease, caused by a deficiency of branched chain α-ketoacid dehydrogenase, is described in Maple Syrup Urine Disease (Branched-Chain Ketoaciduria). Isovaleryl-CoA derived from leucine, 2-methylbutyryl-CoA derived from isoleucine, and isobutyryl-CoA derived from valine are metabolized by separate pathways to intermediates which enter general metabolism. Defects in these pathways cause 13 known metabolic disorders termed branched chain organic acidurias. Several other disorders characterized by branched chain organic aciduria unrelated to branched chain amino acid metabolism are also reviewed in this chapter (Table 122-1).

Table 122-1

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