Maple syrup urine disease is due to deficiency of
METABOLIC DISORDERS OF BRANCHED-CHAIN AMINO ACID CATABOLISMAs the name implies, the odor of urine in maple syrup urine disease (branched-chain ketonuria, or MSUD) suggests maple syrup, or burnt sugar.The biochemical defect in MSUD involves the a-keto acid decarboxylase complex Plasma and urinary levels of leucine, isoleucine, valine, and their a-keto acids and a-hydroxy acids (reduced a-keto acids) are elevated, but the urinary keto acids derive principally from leucine.Signs and symptoms of MSUD include often fatal ketoacidosis, neurological derangements, mental retardation, and a maple syrup odor of urine.The mechanism of toxicity is unknown.Early diagnosis by enzymatic analysis is essential to avoid brain damage and early moality by replacing dietary protein by an amino acid mixture that lacks leucine, isoleucine, and valine.The molecular genetics of MSUD are heterogeneous. MSUD can result from mutations in the genes that encode E1a, E1b, E2, and E3. Based on the locus affected, genetic subtypesof MSUD are recognized.Type IA MSUD arises from mutations in the E1a gene, type IB in the E1b gene, type II in the E2 gene, and type III in the E3 geneReference: Harper biochemistry page no 309
Decarboxylation
Dehydroxylation
Transamination
Deamination
miscellaneous