branched chain ketoaciduria (br ncht)n. |
branched chain ketoaciduria.
Maple Syrup Urine Disease
A rare autosomal recessive [MIM 248600] inborn error of metabolism due to decreased branched-chain -keto acid dehydrogenase complex activity, resulting in defective amino acid metabolism, characterised by urine that smells like maple syrup
Frequency General population 1:200,000; in Pennsylvania Mennonites of German descent 1:176
Pathogenesis The defect in oxidative decarboxylation of branched chain amino acids—BCAA—valine, leucine and isoleucine results in accumulation of BCAA
Lab Increased BCAA, decreased threonine, serine, alanine in urine and serum, positive dinitro-phenylhydrazine test for alpha-keto amino acids, which form insoluble hydrazines
Management Dietary decrease of BCAA, plus dietary overload—20-fold excess of thiamine
Prognosis Mortality was 100%, often due to intercurrent infection; with BCAA-free infant formulas, the survival is ±100% and mental retardation completely preventable; since acute decompensation by BCAA and BCKA is due to a breakdown of endogenous proteins resulting in metabolic acidosis, ketosis, anorexia, emesis and potentially fatal encephalopathy, patients may respond to parenteral solutions of BCAA-free amino acids
Frequency General population 1:200,000; in Pennsylvania Mennonites of German descent 1:176
Pathogenesis The defect in oxidative decarboxylation of branched chain amino acids—BCAA—valine, leucine and isoleucine results in accumulation of BCAA
Lab Increased BCAA, decreased threonine, serine, alanine in urine and serum, positive dinitro-phenylhydrazine test for alpha-keto amino acids, which form insoluble hydrazines
Management Dietary decrease of BCAA, plus dietary overload—20-fold excess of thiamine
Prognosis Mortality was 100%, often due to intercurrent infection; with BCAA-free infant formulas, the survival is ±100% and mental retardation completely preventable; since acute decompensation by BCAA and BCKA is due to a breakdown of endogenous proteins resulting in metabolic acidosis, ketosis, anorexia, emesis and potentially fatal encephalopathy, patients may respond to parenteral solutions of BCAA-free amino acids
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