Scientists at the National Institutes of Health (NIH) National Institute of Environmental Health Sciences (NIEHS) have determined that there may be an association between ultraviolet (UV) radiation from sunlight and some autoimmune diseases, especially in women. The study is the first to evaluate and find a possible UV radiation association in autoimmune diseases in women.
The researchers worked with myositis centers across the country that had seen 380 patients who had been diagnosed with dermatomyositis or polymyositis, the two major forms of myositis, an autoimmune disease in which the body's immune system attacks muscle or skin and sometimes other tissues. Dermatomyositis is typically accompanied by a distinctive reddish-purple rash on the upper eyelids or over the knuckles. It is often made worse with sun exposure.
According to Frederick W. Miller, M.D., Ph.D., chief of the NIEHS Environmental Autoimmunity Group, Program of Clinical Research, the study found that women who lived in areas with higher levels of UV exposure when they developed myositis were more likely to develop the form known as dermatomyositis instead of the form called polymyositis that does not have a rash. He said, "Although we have not shown a direct cause and effect link between UV exposure and this particular autoimmune disease, this study confirms the association between UV levels and the frequency of dermatomyositis that we found in a previous investigation."
Dr. Miller said that the researchers found the association between UV exposure and dermatomyositis only in women and not in men. He remarked that, while women are more likely than men to develop many autoimmune diseases, the reasons for this have not been clear. "It could be that inherent differences in how women and men respond to UV radiation may play a role in the development of certain autoimmune diseases," he observed.
"Patients with autoimmune diseases make a variety of autoantibodies that are unique to different conditions," Dr. Miller said. "One autoantibody specifically associated with dermatomyositis is called the anti-Mi-2 autoantibody, and we know from our previous research that UV radiation increases levels of the Mi-2 protein that this autoantibody binds to."
In addition to finding an association between the level of UV radiation and the proportion of women who developed dermatomyositis compared to polymyositis, the researchers found an association between UV levels and the proportion of women with the anti-Mi-2 autoantibody.
NIEHS Director Linda Birnbaum, Ph.D., commented, "This study adds UV radiation to the growing list of environmental exposures possibly important in the development of autoimmune diseases."
--Source: "Sun Exposure May Trigger Certain Autoimmune Diseases in Women," National Institute of Environmental Health Sciences (NIEHS), via Newswise, July 30, 2009; reference "Ultraviolet Radiation Intensity Predicts the Relative Distribution of Dermatomyositis and Anti-Mi-2 Autoantibodies in Women," Arthritis & Rheumatism, August 2009
