In total, these data demonstrate that, due to loss of HCFC1 or RONIN function, and reduced Mmachc target gene expression, the Hcfc1A115V/Y and RoninF80L/F80L mice are bona fide models of combined methylmalonic acidemia and homocystinuria (Fig. 2i). Here, HCFC1 is linked to methylmalonic acidemia.