An autosomal recessive inborn disorder of cobalamin metabolism caused by biallelic variants in MMADHC. Depending on the type and location of variants in MMADHC, patients may present with methylmalonic aciduria, homocystinuria, or both. MMADHC has been reported to result in the cblD complementation group of cobalamin disorders. The disease is methylmalonic aciduria and/or homocystinuria, cblD type (MONDO_0100463).