Finally, although the biochemical data presented here indicates reduced or absent protein levels in liver cells derived from individuals with MSUD as well as reduced BCKDH activity (represented by elevated branched‐chain alpha‐ketoacids), it cannot be completely ruled out that the variants under investigation are the cause of these biochemical features without a transgenic experiment attempting to rescue a DBT null cell type with a genetic construct that includes these variants. This evidence concerns the gene PPM1K and maple syrup urine disease.