Examining Assumptions about Female Dominance in Autoimmune Disease

Autoimmune diseases are generally increasing in the United States and many other countries, for poorly understood reasons, affecting tens of millions of people. 1 Environmental factors are among the suspects behind these diseases, because genetic factors alone can't explain the significant rise in recent decades of diseases such as multiple sclerosis, Crohn disease, systemic lupus erythematosus, and type 1 diabetes. One common assumption that many experts have adopted, based on evidence pieced together over the decades, is that females are affected more than males by autoimmune diseases. But the key assumption that females are more susceptible to autoimmune diseases may be wrong in certain circumstances, says J. Michael Pollard, an associate professor of molecular medicine at the A number of autoimmune diseases do have a female predominance overall, Pollard says. However, after reviewing selected studies of autoimmune diseases with links to any of more than a dozen known or suspected environmental factors, he found that the presumed female predominance in many autoimmune disorders may be correct in fewer instances than thought; the link is unclear in other situations and may simply not exist in still others. 4 Pollard does not disagree with the sex bias found for idiopathic autoimmune diseases (those for which a cause is unknown). " The question addressed in my review was, is the. .. bias in idiopathic autoim-mune disease also reflected in studies in which an associated environmental exposure has been studied? " he says. One reason for the potentially misleading evidence could be confounding factors such as sex-biased activities. For instance, Pollard found that some evidence reflects the female predominance for an exposure source, as with certain cosmetics and the diseases lupus and rheumatoid arthritis. In a reverse example, he found that the apparent male predominance of several autoimmune diseases resulting from silica exposure could reflect males' dominating the occupations where this exposure tends to occur (e.g., mining and masonry). That became clearer after he identified a study of female subjects that found a relative risk for rheumatoid arthritis from silica exposure even greater than the composite average for males as reported in a meta-analysis of 10 studies. In other studies, Pollard found mixed evidence for predominance by one sex or the other, with results depending on the details. For instance, for lupus caused by prescription drugs, females are more vulnerable when using procainamide (a heart medication), but use of chlorpromazine (an antipsychotic) is linked …