New disorder of vitamin B12 metabolism (cobalamin F) presenting as methylmalonic aciduria.
An infant with vitamin B12-responsive methylmalonic aciduria and no homocystinuria or megaloblastic anemia presented with stomatitis, glossitis, convulsions, and developmental delay. Cultured fibroblasts showed defective incorporation of both [14C]5-methyltetrahydrofolate and [14C]propionate into protein by whole cells and a decrease of methionine synthase activity in cell extracts. Despite excessive incorporation of [57Co]cyano-B12 by fibroblasts from the patient, free vitamin B12 was unable to efflux from lysosomes, and, therefore, synthesis of both adenosyl-B12 and methyl-B12 was impaired.
D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007231:Infant, Newborn; D008314:Malonates / Q000378:metabolism / Q000652:urine*; D008661:Metabolism, Inborn Errors / Q000652:urine*; D011422:Propionates / Q000378:metabolism; D014805:Vitamin B 12 / Q000378:metabolism*
D008314:Malonates; D011422:Propionates; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; C005230:methyl malonate; D014805:Vitamin B 12