MMAA and Methylmalonic aciduria: Isolated methylmalonic aciduria (MMA) is a group of autosomal recessive disorders caused by mutations in the genes MMUT, MMAA, MMAB and MMADHC. Depending on the causative gene and – in case of MMUT – residual methylmalonyl-CoA mutase (MMUT; EC 5.4.99.2) enzyme activity, the MMA subtypes are called mut0, mut-, cblA, cblB, cblD-variant 2 (1).