Recently, a N-ethyl-N-nitrosourea (ENU)-induced mutant mouse that phenotypically resembles human MSUD has been described [20]. However, the mutation in this model disrupts a splice site in the mitochondrial branched-chain aminotransferase (BCAT) gene, not in BCKDH, the deficient enzyme in MSUD. Because the mutation is not in BCKDH, the validity of this mutant mouse line for modeling human MSUD is questionable.