PPM1K and maple syrup urine disease: Maple syrup urine disease (MSUD, MIM #248600) is a recessively inherited inborn error of metabolism characterized by a deficiency of the branched-chain alpha-keto acid dehydrogenase (BCKDH) complex that results in accumulation of branched-chain amino acids (BCAA) including leucine, isoleucine, and valine [1].