Although six genes (BCKDHA, BCKDHB, BCKDK, DBT, DLD and PPM1K) involved in BCAA metabolism have been reported, MSUD is predominantly caused by mutations in the BCKDHA, BCKDHB, and DBT genes encoding the E1α, E1β, and E2 subunits of the BCKD complex, respectively [11]. Here, PPM1K is linked to maple syrup urine disease.