PPM1K and maple syrup urine disease: Besides mutations in BCKDH itself, mutations in PPM1K and BDK were found to cause mild MSUD (Oyarzabal et al. 2013; Maguolo et al. 2022; Ozcelik et al. 2023) and novel mutations are found quite frequently (Sun et al. 2020; Margutti et al. 2020; Medina et al. 2021; Fang et al. 2021; Li et al. 2023; Lashkarian and Salmani 2023).