Women are more susceptible than men to most autoimmune diseases. Some studies estimate that as many as 75 percent of patients with an autoimmune disease are women. When all of these types of diseases are grouped together, deaths from autoimmune diseases are among the top 10 causes of death for women under the age of 65.

However, the prevalence of specific autoimmune diseases varies by sex. More than 85 percent of patients with thyroiditis, scleroderma and lupus are women. In contrast, type 1 diabetes occurs in both sexes at about the same rate.

Autoimmune diseases can affect all races and ethnic groups, but the prevalence varies according to the specific condition.

The causes of autoimmune diseases are not completely understood. Many years of scientific research have focused on the role of the immune system in initiating an attack on the body’s own cells. The results appear to indicate that autoimmune diseases result from a combination of factors.

Genetics play a major role in the development of certain autoimmune diseases. For type 1 diabetes, as well as other autoimmune diseases, an increased risk is seen in certain families. For example, identical twins share the same genes. Thus, when one twin has an autoimmune disease, the other twin has a 15 to 50 percent chance of developing the same disease (an average of a 30 percent chance). In comparison, non-identical twins and other siblings have a 2 to 5 percent chance of developing the disease.

Researchers are exploring which genes may be responsible for autoimmune diseases. The majority of autoimmune disease appear to result from the effects of multiple genes acting together to disrupt immune system function. In addition, an individual with one autoimmune disease has an increased risk of developing another. This may mean that some of the genetic mechanisms that increase a person’s susceptibility are common to multiple autoimmune diseases.

Genetics is not the only contributor to the development of autoimmune diseases – exposure to toxins and environmental factors are also important. There is evidence that certain medications, heavy metals, other pollutants and ultraviolet light from the sun may have a role. Deficiencies in micronutrients such as antioxidants and the mineral selenium may also contribute.

Scientific evidence indicates that many autoimmune diseases can be triggered by a preceding infection. For example, the Epstein-Barr, rubella and mumps viruses are among the infectious diseases that have all been implicated in the development of autoimmune diseases in some people. These and other infectious antigens may resemble proteins of normal body cells. After the immune system fights these viral infections, it may mistake the healthy body cells for the antigens.