Of the 20 mother-infant pairs with concentrations >310 pmol/L, 80% of infants had serum vitamin B-12 concentrations considered adequate, 15% of infants had serum vitamin B-12 concentrations considered marginal, and 1 infant had a serum vitamin B-12 concentration indicating deficiency. This evidence concerns the gene SPRR2A and hyperinsulinemic hypoglycemia, familial, 4.