The association of vitamin B12 deficiency and benign familial infantile convulsions (BFIC) is reported in one 4-month-old boy admitted to the University Hospital, Lund, Sweden, and in an additional 4 of 14 infants with BFIC who were found to have homocysteinuria or methylmalonic aciduria. The 4-mo-old presented with generalized tonic-clonic convulsions, partially responsive to vigabatrin. CT and initial EEGs were normal, and an ictal recording showed epileptiform activity over the left frontal region. Laboratory investigations were normal except for absent plasma cobalamin levels (<75 pmol/1), elevated plasma homocysteine (16.5 mcmol/1; N 5.3-11.0) and methylmalonic acid (0.88 mcmol/1; N<0.42), consistent with a diagnosis of vitamin B12 deficiency. The mother had anemia treated with intramuscular ferritin-sorbitol during the pregnancy. The infant received oral vitamin B12, 0.5 mg every 3 d, and seizures were controlled, except for a convulsion with fever. Treatment was discontinued at 7-12 months when laboratory tests were normal, and at 1.5 year follow-up, seizures had not recurred and development was normal. 
COMMENT. Infants of vegetarian mothers or those suffering from pernicious anemia may develop vitamin B12 deficiency in early infancy, leading to convulsions in susceptible infants. In the present case-report, the cause of the vitamin B12 deficiency is undetermined, but a genetic error in B12 metabolism cannot be excluded. The familial incidence of benign familial infantile convulsions (BFIC) indicates a genetic etiology, with linkage analysis mapped to chromosome 19. Environmental influences involving vitamin B12 metabolism in the mother and deficiency in the infant are also causative.
Infants with seizures in the first year of life should be examined for homocysteine and methylmalonic acid elevations in the plasma and a transient vitamin B12 deficiency, responsive to vitamin supplementation. Vitamin B12 is a co-factor in methionine synthatase and methylmalonyl-CoA-mutase, a deficiency leading to the accumulation of homocysteine and methylmalonate in the plasma.