People with rheumatoid arthritis (RA) or other autoimmune diseases have a high likelihood of being impacted with a second autoimmune disorder. The question is why?
Several explanations for the phenomenon were offered in a recent news report that presented data from multiple studies on the co-occurrence of autoimmune diseases.
Some studies suggested that genetic and immunologic mechanisms may contribute to co-existing autoimmune diseases. Environmental triggers may also set the manifestation of a second disease in motion.
There is strong evidence that autoimmune disorders share several symptoms, immune changes, and genetic factors. This indicates that they could have a common origin, which has stimulated research to find common genetic roots.
Polyautoimmunity is defined as the presence of more than one autoimmune disease in the same patient. The occurrence of three or more autoimmune diseases, however, is called multiple autoimmune syndrome (MAS). According to researchers, the syndrome may be more prevalent than previously thought.
Dr. Regina Berkovich, PhD, an assistant professor at the University of Southern California, explained that the main reason autoimmune disorders tend to coincide lies in the already faulty immune system. An immune system following an autoimmune pattern simply creates more possibility for other targets.
According to Emily C. Somers,PhD, an associate professor of internal medicine, environmental health sciences, and obstetrics and gynecology at the University of Michigan, genetic factors could be in play.
Somers investigated the risk for co-existence of RA, autoimmune thyroiditis, MS, and diabetes mellitus and observed a higher rate of RA among women with diabetes. Researchers noted that both diseases were among the most common autoimmune diseases in the general population. RA and autoimmune thyroiditis tended to occur together also.
The opposite relationship occurred between RA and MS. When a patient displayed one of the disorders, the likelihood of having the other was decreased. According to Somers, there is no firm explanation for those odds but it has been reported that when genetic variants increased patient vulnerability for one of these diseases there was decreased likelihood for the other one.
“Over the last decade, several genetic factors have been found in common between multiple autoimmune diseases,” Somers said in a news release. “However, the particular combinations of genetic and environmental factors will influence the way that autoimmunity is expressed.”
Researchers emphasize that the possibility of patients dealing with two one autoimmune disease at the same time should be important to clinicians.
“The practical clinical implications of the clustering could include making clinicians aware of certain associations, such as RA and Sjögrens syndrome as they follow patients,” said Eric Matteson, a rheumatologist at the Mayo Clinic. “This may be helpful in unraveling some of the common pathophysiological basis for these diseases.”