Pernicious anemia (also known as Biermer's anemia, Addison's anemia, or Addison–Biermer anemia) is one of many types of the larger family of megaloblastic anemias. It is caused by loss of gastric parietal cells, and subsequent inability to absorb vitamin B12. Usually seated in an atrophic gastritis, the autoimmune destruction of gastric parietal cells leads to a lack of intrinsic factor. Since the absorption from the gut of normal dietary amounts of vitamin B12 is dependent on intrinsic factor, the loss of intrinsic factor leads to vitamin B12 deficiency...