Addison's anemia is a blood disorder resulting from a deficiency that prevents patients from producing a necessary gastric substance for absorbing vitamin B12. This substance is known as intrinsic factor (IF). Today, this condition is more commonly referred to as pernicious anemia (PA). It is marked by the presence of large, immature, nucleated cells called megaloblasts, which are precursors to mature red blood cells. These mature cells typically lack nuclei, making PA a type of megaloblastic anemia.The first description of PA, though not named as such, was by English physician Thomas Addison in 1855. He labeled it as a consistently fatal "idiopathic anemia," acknowledging the unknown cause of the illness. The term "pernicious anemia" was introduced in 1872 by German physician Anton Biermer, whose work on the disease surpassed Addison's original description. The research by George H. Whipple on liver's effects in anemia, and subsequent studies by George R. Minot and Wm. P. Murphy specifically on PA, led to the discovery of a cure through liver consumption, earning them the Nobel Prize in 1934.Today, PA is no longer life-threatening. It is treated with vitamin B12 injections, as individuals with PA lack the IF necessary for oral absorption of the vitamin. There is evidence suggesting a genetic component to PA, although its inheritance pattern is not well-documented. A hereditary form of PA, caused by a defect in IF, is clearly inherited as an autosomal recessive trait, with the affected individual inheriting one gene from each parent. The gene for IF is located on human chromosome 11.The term "pernicious" implies something highly damaging, destructive, or deadly, originating from the Latin root "nex," meaning "violent death." While pernicious anemia was once fatal, it is fortunately manageable today. PA has also been known by other names and terms.