The importance of the MUT‐catalyzed reaction is further underlined by the metabolic disorder methylmalonic aciduria (MMA), which is caused by a genetic defect in the MUT enzyme itself (MIM# 251000, MMA mut type), or in one of several proteins (MMAA, MMAB, MMADHC) involved in the uptake, modification, and delivery of AdoCbl to the MUT enzyme for its activity (MMA cblA type, MIM# 251100; MMA cblB type, MIM# 251110; MMA cblD‐variant 2 MIM# 277410) [Fowler et al., 2008]. Here, MMUT is linked to Other metabolic disease.