Intracellular cobalamin (IC) and its two coenzymes, adenosylcobalamin and methylcobalamin, are necessary for the homeostasis of methylmalonic acid and homocysteine (Hcy). Defects of intracellular cobalamin metabolism are responsible for isolated methylmalonic aciduria (MMA), isolated increased Hcy, or both. MMA occurs when adenosylcobalamin, a cofactor of methylmalonic-CoA mutase, is low, thereby causing elevated MMA and decreased succinyl-CoA. A lack of methylcobalamin, a cofactor for methionine synthase, impairs the transformation of Hcy into methionine, thus leading to increased Hcy and low methionine levels.
Key words
Methylmalonic acid, cobalamin metabolism