A blood Anemia, addisonian: A blood disorder caused by a lack of vitamin B12. Patients who have this disorder do not produce the substance in the stomach that allows the body to absorb vitamin B12. This substance is called intrinsic factor (IF).Addisonian anemia, better known today as pernicious anemia (PA), is characterized by the presence in the blood of large, immature, nucleated cells (megaloblasts) that are forerunners of red blood cells. (Red blood cells, when mature, have no nucleus). It is thus a type of megaloblastic anemia. Pernicious anemia (PA) was first described (although not by that name) in 1855 by the English physician Thomas Addison. He called it an invariably fatal "idiopathic anemia." The "idiopathic" was a frank admission that the cause of this illness was wholly unknown. The name "pernicious anemia" was coined in 1872 by the German physician Anton Biermer whose description of the disease was superior to that of Addison. The studies of George H. Whipple on the effects of feeding liver in anemia followed by those of George R. Minot and Wm. P. Murphy on the effects of feeding liver specifically in pernicious anemia (PA) led to the cure of PA and to their receiving the Nobel Prize in 1934. Nowadays PA is an unpernicious anemia. It is simply treated with vitamin B12. The vitamin B12 has to be administered by injection (parenterally) because people with PA do not have IF (or an effective form of IF) and so cannot absorb vitamin B12 taken by mouth. There is some evidence that PA may be genetic although its mode of inheritance is poorly documented. There is a congenital form of PA due to defect of IF that is clearly inherited as an autosomal recessive trait with the affected child having received two copies of the gene, one from each parent. The IF gene itself has been localized to human chromosome 11.The word "pernicious" means highly injurious, destructive, or deadly. "Pernicious" comes from the Latin root "nex" meaning "violent death." Pernicious anemia was once quite deadly. Today it fortunately is not. PA has also been called Addison's anemia and Biermer's anemia.