Autoimmune diseases occur when the body's immune system malfunctions and mistakenly attacks healthy cells, tissues, and organs. Strong data on the incidence and prevalence of autoimmune diseases are limited, but a 2009 study estimated the prevalence of autoimmune diseases in the U.S. to be 7.6 to 9.4 percent, or 25 to 31 million people today. This estimate, however, includes only 29 autoimmune diseases, and it does not account for increases in...