| February 15th, 2024byDr. Monica M. Bertagnolli As many as 50 million Americans have one of more than 100 knownautoimmune diseases, making it the third most prevalent disease category, surpassed only by cancer and heart disease.1,2This category of disease has also long held a mystery: Why are most people with a chronic autoimmune conditionas many as four out of every fivewomen? This sex-biased trend includes autoimmune diseases such asrheumatoid arthritis,multiple sclerosis,scleroderma,lupus,Sjgrens syndrome, and many others. Now, exciting findings from astudysupported in part by NIH provide a clue to why this may be the case, with potentially important implications for the early detection, treatment, and prevention of autoimmune diseases. The new evidence, reported in the journalCell, suggests that more women develop autoimmune diseases than men due in part to the most fundamental difference between the biological sexes: that females have two X chromosomes, while males have an X and a Y. More specifically, it has to do with molecules called Xist (pronounced exist), which are encoded on the X chromosome and transcribed into long non-coding stretches of RNA, only when there are two X chromosomes. | 