Study Offers New Clues to Why Most People with Autoimmune Diseases Are Women

Posted on February 15th, 2024 by Dr. Monica M. Bertagnolli

As many as 50 million Americans have one of more than 100 known autoimmune diseases, making it the third most prevalent disease category, surpassed only by cancer and heart disease.^1,2 This category of disease has also long held a mystery: Why are most people with a chronic autoimmune condition—as many as four out of every five—women? This sex-biased trend includes autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, scleroderma, lupus, Sjögren’s syndrome, and many others.

Now, exciting findings from a study supported 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 journal Cell, 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.

Those long Xist molecules wind themselves around sections of just one of a female’s two X chromosomes, shutting down the extra X chromosome in a process known as X-chromosome inactivation. It’s an essential process to ensure those cells won’t produce too many proteins encoded on X chromosomes, which would be a deadly mistake. It’s also something that males, with a single X chromosome and much smaller Y chromosome carrying almost no working genes, don’t have to worry about.

The new findings come from a team at Stanford University School of Medicine, Stanford, CA, led by Howard Chang and Diana Dou. What they suggest is that while Xist molecules play an essential role in X-chromosome inactivation, they also have a more nefarious ability to encourage the formation of odd clumps of RNA, DNA, and proteins that can in turn trigger strong autoimmune responses.

In earlier research, the team identified about 80 different proteins that bind to Xist either directly or indirectly. After taking a close look at the list, the researchers realized that many of the proteins had been shown to play some role in autoimmune conditions. This raised an intriguing question: Could the reason women develop autoimmune diseases so much more often than men be explained by those Xist-containing clumps?

To test the idea, the researchers first decided to study it in male mice. They made two different strains of male mice produce Xist to see if it would increase their risk for autoimmunity in ways they could measure. And it did. The researchers found that once Xist was activated in male mice that were genetically prone to autoimmunity, they became more susceptible to developing a lupus-like condition. It didn’t happen in every individual, which suggests, not surprisingly, that the development of autoimmune disease requires additional triggers as well.

In addition, in a different mouse strain that was resistant to developing autoimmunity, the addition of Xist in males wasn’t enough to cause autoimmunity, the researchers found. That also makes sense in that, while women are much more prone to developing autoimmune disease, most people don’t. Xist complexes likely lead to autoimmunity only when certain genetic and other factors are met.

The researchers also examined blood samples from 100 people with autoimmune conditions and found they had antibodies to many of their own Xist complexes. Some of those antibodies also appeared specific to a certain autoimmune disorder, suggesting that they might be useful for tests that could detect autoimmunity or particular autoimmune conditions even before symptoms arise.

There are still many questions to explore in future research, including why men sometimes do get autoimmune conditions, and what other key triggers drive the development of autoimmunity. But this fundamentally important discovery points to potentially new ways to think about the causes for the autoimmune conditions that affect so many people in communities here and around the world.

References:

[1] The American Autoimmune Related Diseases Association. Autoimmune Facts.

[2] Dou DR, et al. Xist ribonucleoproteins promote female sex-biased autoimmunity. Cell. DOI: 10.1016/j.cell.2023.12.037. (2024).

NIH Support: National Institute of Arthritis and Musculoskeletal and Skin Diseases