The Inactive X Chromosome: A Genetic Driver of Female-Biased Rheumatic Autoimmune Disorders?

Females have a better ability to resolve infections compared to males, but also a greater susceptibility to develop autoimmunity. Besides the initial interest in the contribution of sex-steroid hormone signaling, the role of genetic factors linked to the X chromosome has recently received much attention. In humans and mice, the number of X chromosomes, rather than sex-steroid hormones, is associated with a higher risk to develop autoimmunity, particularly rheumatic diseases, such as SLE, Sjögren's syndrome, or systemic sclerosis. In this review, we will summarize the recent advances in the various mechanisms and pathways involving the X chromosome in female sex-biased autoimmune diseases. We will particularly focus on the experimental evidence suggesting that expression of X-linked genes due to dysregulation in X chromosome inactivation maintenance could contribute to the female predisposition for autoautoimmunity.