Women have two X chromosomes, while men have an X and a Y chromosome. Every female experiences something known as X chromosome inactivation, where one of the two X chromosomes is silenced by a molecule called Xist to prevent harmful effects of producing twice the amount of X-linked genes. Many proteins that attach to the Xist molecule, along with the Xist molecule itself, are known targets of autoantibodies, which could explain why lupus is more common in women.