PPM1K and maple syrup urine disease: Maple Syrup Urine Disease (MSUD) is an inherited disorder in branched-chain amino acid (BCAA) catabolism caused by mutations in genes that encode the components of the branched chain keto-acid dehydrogenase (BCKDH) complex, which catalyzes the first irreversible step in BCAA catabolism1, 2, 3.