Description
Biermer´s anaemia or pernicious anaemia is the most common cause of vitamin B12 deficiency in Western populations showing the classical features of megaloblastic anemia (i.e. morphologic and functional abnormalities of the blood cells and marrow precursors related to impairment of DNA synthesis). It is characterised by a gastric mucosal defect that decreases the synthesis of intrinsic factor and the occurrence of autoantibodies to gastric parietal cells and to intrinsic factor. Human intrinsic factor is a glycoprotein that is exclusively produced by gastric parietal cells. It plays an essential role in the absorption and transport of vitamin B12 across the small intestine. Two types of intrinsic factor autoantibodies exist. Type I antibodies block the cobalamin binding site on the intrinsic factor molecule, preventing uptake of the vitamin. Type II antibodies block a different site of the intrinsic factor molecule that is involved in binding of the intrinsic factor-cobalamincomplex to ileal receptors. Both types of antibodies have the same pathological effect, i.e. preventing cobalamin resorption by ileal receptors. Serum intrinsic factor autoantibodies can be detected in 50 to 70% of pernicious anaemia patients and are highly specific for Biermer´s anemia with no reported single true positive in a healthy control. Intrinsic Factor Ab ELISA detects both types of autoantibodies and thereby provides a useful tool in the differential diagnosis of pernicious anaemia and other causes of vitamin B12 malabsorption