Genetic defects of cobalamin metabolism.

As a consequence of investigations on the pathogenesis of an inborn error of metabolism characterized by increased urinary and plasma levels of methylmalonic acid, the metabolism of vitamin B12 and its functional roles have become elucidated. Four human mutations have been identified in which a defect in the metabolism of deoxyadenosinecobalamin or methylcobalamin occurs. These investigations have highlighted the functional significance of co-factors or coenzymes in the maintenance of health and have identified new approaches for the treatment of genetic diseases involving the use of pharmacologic doses of vitamins.