ENU mutagenesis identifies mice with mitochondrial branched-chain aminotransferase deficiency resembling human maple syrup urine disease

J Clin Invest. 2004 Feb;113(3):434-40. doi: 10.1172/JCI19574.


Tandem mass spectrometry was applied to detect derangements in the pathways of amino acid and fatty acid metabolism in N-ethyl-N-nitrosourea-treated (ENU-treated) mice. We identified mice with marked elevation of blood branched-chain amino acids (BCAAs), ketoaciduria, and clinical features resembling human maple syrup urine disease (MSUD), a severe genetic metabolic disorder caused by the deficiency of branched-chain alpha-keto acid dehydrogenase (BCKD) complex. However, the BCKD genes and enzyme activity were normal. Sequencing of branched-chain aminotransferase genes (Bcat) showed no mutation in the cytoplasmic isoform (Bcat-1) but revealed a homozygous splice site mutation in the mitochondrial isoform (Bcat-2). The mutation caused a deletion of exon 2, a marked decrease in Bcat-2 mRNA, and a deficiency in both BCAT-2 protein and its enzyme activity. Affected mice responded to a BCAA-restricted diet with amelioration of the clinical symptoms and normalization of the amino acid pattern. We conclude that BCAT-2 deficiency in the mouse can cause a disease that mimics human MSUD. These mice provide an important animal model for study of BCAA metabolism and its toxicity. Metabolomics-guided screening, coupled with ENU mutagenesis, is a powerful approach in uncovering novel enzyme deficiencies and recognizing important pathways of genetic metabolic disorders.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acids, Branched-Chain / metabolism
  • Animals
  • Base Sequence
  • Disease Models, Animal
  • Ethylnitrosourea / pharmacology
  • Humans
  • Maple Syrup Urine Disease / enzymology*
  • Maple Syrup Urine Disease / genetics
  • Mass Spectrometry
  • Mice
  • Mitochondria / enzymology*
  • Mitochondria / metabolism
  • Molecular Sequence Data
  • Mutagens / pharmacology
  • Mutation*
  • Transaminases / deficiency*
  • Transaminases / drug effects
  • Transaminases / genetics


  • Amino Acids, Branched-Chain
  • Mutagens
  • Transaminases
  • branched-chain-amino-acid transaminase
  • Ethylnitrosourea