You may be able blame Mom for this one. Chances are if you have this common autoimmune disorder that can cause swelling and stiffness of the joints it’s in your genes. So if your mom (or dad or other close relative) has rheumatoid arthritis (RA), you are more likely to suffer from it too. But as it often goes with nature, it’s complicated. Heredity only raises your risk by about 20 percent, explains Weijia Yuan, M.D., a rheumatologist at the Hospital for Special Surgery in New York. A secondary factor—a trigger—may be needed to activate the disease.