It all comes down to genetics.

Sick woman
Sick woman
| Credit: Eugenio Marongiu / Getty Images

When it comes to autoimmune diseases, women without a doubt get the short end of the stick. Nearly 80% of people who suffer from autoimmune diseases are women, and until very recently, scientists had no idea why. But new research may hold the answer, and the culprit is about as deep-seated as they come: our genes.

Historically, research on why women are so disproportionately affected by disorders like psoriasis, Crohn's disease, and rheumatoid arthritis has focused on sex hormones, like estrogen and testosterone. However, a new study published in the journal Nature Immunology took an entirely new approach, and as Health reports, the results are eye-opening.

"We found a completely new angle," says senior author Johann Gudjonsson, M.D., Ph.D., University of Michigan assistant professor of dermatology in a release. "Our team identified a gene expression difference between the sexes that is associated with susceptibility to autoimmune disease."

Basically, there's something hardwired into a women's DNA that makes them more susceptible to developing an autoimmune disease. Autoimmune disorders like psoriasis and lupus occur when the body's immune system overreacts, and in turn attacks itself, flooding the body with inflammatory proteins that can harm vital organs.

In their study, Gudjonsson and his team focused on autoimmune diseases of the skin, including psoriasis and lupus. (Although lupus affects the whole body, four of the 11 criteria for diagnosis relate to the skin.) After analyzing genetic material from skin samples of 82 healthy men and women, they discovered a whopping 661 genes that were expressed differently in women versus men. Many of these are already known to be involved in immune function, and some have been linked to autoimmune disease.

"This finding suggested that these sex-biased genes contributed to not only increased disease susceptibility but possibly also heightened disease activity," the researchers wrote. "In this context, we note that being female is the strongest risk factor for the development of autoimmunity, and it dwarfs the identified autoimmune genetic risk variants."

Even more notable was their ability to identify one protein, called VGLL3, as a "master regulator" of inflammation and autoimmunity. In healthy skin samples, researchers found that VGLL3 was only active in women.

The authors suggest that these genes and proteins may one day be useful in assessing who's most at risk for autoimmune diseases, or for identifying targets for new medications. "Learning more about these disease processes in each gender will provide opportunities for therapeutic interventions we did not imagine before," said Dr. Gudjonsson, "including both prevention and treatment."