Selective vitamin B12 malabsorption in two siblings.

Two siblings with megaloblastic anemia responsive to parenteral vitamin B(12) were studied to elucidate the cause of the B(12) deficiency. Gastric juice from both contained acid and functional intrinsic factor. Serum contained transcobalamin II and lacked antibodies to intrinsic factor. Schilling tests showed vitamin B(12) malabsorption uncorrected by hog intrinsic factor or pancreatic extract. Other parameters of small intestinal function were normal. Proteinuria was initially present in both but cleared in one following treatment with B(12). These patients with "familial selective vitamin B(12) malabsorption" are the first reported from Canada. Only 37 cases have been reported in the world literature to date.