While researchers do not yet know exactly what triggers the development of autoimmune diseases, there are some factors that tend to increase your risk of developing one. In particular, women are as much as three times as likely as men to develop some type of autoimmune disease, and for certain autoimmune diseases the ratio of females to males with the disease is as high as nine to one. Most autoimmune diseases tend to run in families, meaning you are more likely to develop the disease if you have a close relative with that disease. For some autoimmune diseases this familial risk is small, with the risk of developing the same disease as a parent as low as one to two percent. Others have a much greater tendency to be passed on to children, with a familial risk of five to ten percent or more. Finally, some environmental factors seem to be associated with increased risk of certain autoimmune diseases. For example, MS is much more prevalent in temperate northern latitudes than in dry or tropical southern climes.