Late-onset cobalamin C disease: rare but treatable.

Cobalamin C disease is the most common inborn error of cobalamin metabolism, resulting from mutations in methylmalonic aciduria and homocystinuria type C protein (MMACHC) gene. There is associated elevation of homocysteine and methylmalonic acid and decreased synthesis of methionine. It is a multisystem disorder characterised by cognitive impairment, psychiatric manifestations, haematological manifestations and thromboembolic phenomena. Its variable clinical presentation and wide age distribution at presentation necessitates a high index of diagnostic suspicion. The diagnosis is suggested by amino acid chromatography and confirmed by sequencing analysis of the MMACHC gene Parenteral hydroxycobalamin and betaine can bring significant clinical and biochemical improvement and is the recommended long-term therapy.