Familial Selective Malabsorption of Vitamin B12

The oldest known patient with documented familial selective malabsorption of vitamin B12 was restudied in an attempt to establish the cause of his isolated defect of vitamin B12 absorption. In previous studies an "inhibitor" of intrinsic factor (1959) and, more recently, an antibody to intrinsic factor (1966) were reported to be present in the gastric juice of this patient. In the present study, the gastric juice tested in a bioassay was found to contain a normal amount of biologically active intrinsic factor. Neither antibodies to intrinsic factor nor inhibitors of intrinsic factor were present. The mechanism responsible for vitamin B12 malabsorption in this disorder remains obscure.