According to the involved subunit, MSUD is divided into the following types: (1) type Ia (OMIM 608348), caused by biallelic pathogenic variants in BCKDHA gene encoding the Elα subunit (2) type I b (OMIM 248611), caused by biallelic pathogenic variants in BCKDHB gene encoding the E1β subunit (3) type II (OMlM 248610), caused by biallelic pathogenic variants in DBT gene encoding E2 subunit (4) type III (OMIM 238331), caused by biallelic pathogenic variants in DLD gene encoding E3 subunit7. This evidence concerns the gene BCKDHB and maple syrup urine disease.