Vitamin B12Malabsorption Due to a Biologically Inert Intrinsic Factor

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Abstract
Two recognized congenital causes of vitamin B12 malabsorption are an isolated absence of intrinsic-factor (IF) secretion and a selective ileal absorptive defect. A child, who presented with megaloblastic anemia due to vitamin B12 deficiency, did not absorb free vitamin B12 given orally but absorbed normal quantities given bound to normal human gastric juice. No serum antibodies against IF were demonstrated. Gastric juice was acid and contained normal quantities of immunologically identifiable IF. Gastric biopsy was normal. Tests of small-bowel function gave normal results. Patient gastric juice did not correct the vitamin B12 malabsorption of a totally gastrectomized volunteer, nor did it promote vitamin B12 uptake by homogenates of guinea-pig intestinal mucosa. The affinity of patient IF for vitamin B12 appeared normal. Standard Chromatographic procedures failed to reveal a difference from normal IF. The vitamin B12 malabsorption appears to be due to the secretion of a biologically inert IF.