Cobalamin Malabsorption due to a Dysfunctional Intrinsic Factor

An 18-year-old French Canadian student presenting with a severenormocytic anemia, had undetectable serum cobalamin but normal gastric acidityand no evidence of generalized malabsorption. The gastric juice contained a normalquantity of intrinsic factor. Serum anti-intrinsic factor blocking antibodies were notpresent. Absorption of radiolabelled cobalamin given orally in the Schilling test wasdecreased but this was corrected by using hog intrinsic factor. Patient gastric juicebound cobalamin normally but did not promote uptake of this vitamin by homogenatesof guinea pig intestinal mucosa. A family study showed normal cobalaminabsorption for all tested subjects, as well as two α-hemoglobin gene deletions in thefather and a single α-gene deletion in the patient. The cobalamin malabsorption islikely due to a defect of the patient's intrinsic factor at the ilea! receptor sire