Intrinsic factor congenital deficiency

Vitamin B12 deficiency also occurs when the region of the distal ileum that absorbs the vitamin B12-intrinsic factor complex is damaged, as when the ileum is involved with inflammatory bowel disease, or when the ileum is surgically resected. In these situations, radioactively labeled vitamin B12 is not absorbed in the Schilling test, even when intrinsic factor is added. Other rare causes of vitamin B,2 deficiency include bacterial overgrowth of the small bowel, chronic pancreatitis, and thyroid disease. Rare cases of vitamin B12 deficiency in children have been found to be secondary to congenital deficiency of intrinsic factor and congenital selective vitamin Bi2 malabsorption due to defects of the receptor sites in the distal ileum. 

FIGURE 53-8 The absorption and distribution of vitamin Deficiency of vitamin can result from a congenital or acquired defect in any one of the following (1) inadequate dietary supply (2) inadequate secretion of intrinsic factor (classical pernicious anemia) (3) ileal disease (4) congenital absence of transcobalamin II (Tell) or (5) rapid depletion of hepatic stores by interference with reabsorption of vitamin excreted in bile. The utility of measurements of the concentration of vitamin B 2 tn plasma to estimate supply available to tissues can be compromised by liver disease and (6) the appearance of abnormal amounts of transcobalamins I and III (Tcl and III) in plasma. Finally, the formation of methylcobalamin requires (7) normal transport into cells and an adequate supply of folic acid as CH H PteGlu. ... 

The most frequent cause of cobalamin deficiency is insufficient absorption due to a lack of Intrinsic Factor. This condition is more generally known as pernicious anemia and is caused by the occurrence of autoantibodies against parietal cells and Intrinsic Factor, blocking its capacity to bind cobalamin and preventing its absorption. Less frequent causes are abnormal intestinal flora, partial or total gastrectomy, tropical sprue, fish tapeworm infestation, and the congenital Intrinsic Factor abnormality and Intrinsic Factor receptor dysfunction (Imerslund-Grasbeck disease). 

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