PEDIATRICS Vol. 78 No. 1 July 1986, pp. 51-54
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New Disorder of Vitamin B12 Metabolism (Cobalamin F) Presenting as Methylmalonic Aciduria

David S. Rosenblatt MD1, Rachel Laframboise MD1, Jeanne Pichette MD1, Pierre Langevin MD1, Bernard A. Cooper MD1, and Teresa Costa MD1

1 From the Centre for Human Genetics, MRC Genetics Group, and the Departments of Pediatrics, Biology, Medicine, and Physiology, McGill University, and the Réseau de Médecine Génétique du Québec and the Department of Pediatrics, Le Centre Hospitalier de l'Université Laval, Ste-Foy, Quebec, Canada

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.

Key Words: vitamin B12 • cobalamin F • methylmalonic aciduria

Submitted on July 2, 1985