We studied a six-month-old infant with severe megaloblastic anemia, coma and hyperpigmentation of the extremities. He was found to have methylmalonic aciduria (79 μmol per milligram of creatinine) and homocystinuria (0.85 μmol per milligram of creatinine). Additional biochemical abnormalities included cystathioninuria, glycinuria, methylcitric aciduria, 3-hydroxypropionic aciduria and formic aciduria. The concentration of vitamin B12 in the serum was 20 pg per milliliter. This severe nutritional deficiency was a consequence of inadequate intake, for the infant was exclusively breast-fed by a strictly vegetarian mother who manifested methylmalonic aciduria. Our observations emphasize the importance of educating strict vegetarians about the deficiency of vitamin B12 in their diets and the importance of vitamin B12 supplementation. (N Engl J Med 299:317–323, 1978) THE increasing rarity of nutritional-deficiency disease may create problems in medical diagnosis and management for physicians in developed countries. Vegan diets — those from which animal proteins are strictly excluded — have become increasingly popular. Although rich in many vitamins, these diets are deficient in vitamin B12.1 In the infant described below, striking dysfunction of the hematopoietic and central nervous systems resulted from nutritional deficiency of vitamin B12. The infant had been exclusively breast-fed by a strict vegetarian mother. The presentation of the infant suggested an inborn error of metabolism, and he was found to have.
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