Combined Methylmalonic Aciduria and Homocystinuria

**Semantic type:** Disease or Syndrome

**Definition:** A genetically heterogeneous disorder of cobalamin (cbl; vitamin B12) metabolism due to loss of function mutations in the enzymes that synthesize the coenzymes adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). This is a subtype of methylmalonic acidemia that includes complementation groups cblC, cblD, cblF, cblJ, cblL and cblX.

**Synonyms:** - Combined methylmalonic acidemia and homocystinuria due to defects in adenosylcobalamin and methylcobalamin synthesis