Pernicious anaemia is an autoimmune disease. An autoimmune disease is a condition caused by antibodies from your immune system attacking your body. Your immune system mistakes your own tissue as foreign and attacks it, causing inflammation. If you have pernicious anaemia, the inflammation happens in the lining of your stomach. The exact causes of pernicious anaemia aren't fully understood at present. It tends to run in families and is most common in people of 60 or more, it affects women more than men. If you have another autoimmune disease, such as Addison's disease, you may be more likely to develop pernicious anaemia.
Attribution: BUPA