MMA with homocystinuria can be found in the following complementation groups: cblC (OMIM, 277400), which is caused by mutations in MMACHC (OMIM, 609831); cblD (OMIM, 277410), which is caused by mutations in MMADHC (OMIM, 611935); and cblF (OMIM, 277380), which is caused by mutations in LMBRD1 (OMIM, 612625)9. Here, MMADHC is linked to homocystinuria.