Methylmalonic aciduria and homocystinuria type D protein, mitochondrial also known as MMADHC is a protein that in humans is encoded by the MMADHC gene.
This gene encodes a protein localized in cytosol and mitochondria that is involved in an early step of vitamin B<sub>12</sub> metabolism. Vitamin B<sub>12</sub> (cobalamin) is essential for normal development and survival in humans.
Mutations in this gene cause methylmalonic aciduria and homocystinuria type cblD (MMADHC), a disorder of cobalamin metabolism that is characterized by decreased levels of the coenzymes adenosylcobalamin and methylcobalamin.