What are the causes of pernicious anemia?

Autoimmune disease. Pernicious anemia is an autoimmune disease producing autoantibodies against intrinsic factor found in the lining of the stomach. This leads to lack of absorption of vitamin B12 which is important in making blood cells and for nourishment of the nervous system. Treatment would be by replacement of B12 via injections or absorption into the body by other means (nasal spray).