PPM1K and maple syrup urine disease: Maple Syrup Urine Disease (MSUD) is a genetic disorder caused by a deficiency of branched-chain keto acid dehydrogenase (BCKDH), a mitochondrial multienzyme complex responsible for the oxidative decarboxylation of branched-chain keto acids derived from branched-chain amino acids (BCAA), leucine, isoleucine and valine (for review, see: [1]).