Demyelination and inborn errors of the single carbon transfer pathway.

Inborn errors of the single-carbon transfer pathway are rare disorders of folate and cobalamin metabolism. They may be complicated by demyelination resembling subacute combined degeneration of the cord and brain. The study of CSF metabolites in children with serial errors affecting the single-carbon transfer pathway has suggested that S-adenosylmethionine deficiency is a cause of the demyelination. This deficiency is corrected by treatment that causes clinical improvement and remyelination. Some treatments can only have an indirect effect on the brain and this is discussed with other evidence that the liver may produce factors that are necessary for the maintenance of central myelin.