Rheumatoid arthritis risk among women has always been higher than men, and now a new study finds that women who carry babies could be getting rheumatoid arthritis much more often.

Rheumatoid arthritis has been tied to many factors, including lifestyle choices, diet, and previous infections, but a new study says that harmful cells from fetuses carrying harmful genes from the father may have a lot more to do with it.

According to the study, some versions of the immune system gene HLA-DRB1, known as the shared epitope alleles, could be to blame. These cells are responsible for the immune system’s response to infection and, in transplant medicine, for differentiating between one’s own cells and those that are foreign.

Giovanna Cruz, MS, graduate student at the University of California, Berkeley, and first author on the new study says,

“During pregnancy, you’ll find a small number of fetal cells circulating around the mother’s body, and it seems that in some women, they persist as long as several decades. Women with rheumatoid arthritis are more likely to have this persistence of fetal cells, known as fetal microchimerism, than women without the condition, suggesting that it is a potential risk factor for the development of rheumatoid arthritis.”

“Why it happens, we don’t know, but we suspect HLA genes and their activity may be involved,” she added.

In other words, the body’s immune system could be attacking these leftover cells from a baby, sometimes 20 or 30 years later, causing a reaction in the form of rheumatoid arthritis.

Cruz said, “We don’t yet understand how the shared epitope and other HLA alleles influence rheumatoid arthritis risk, but one possibility is that interactions between the proteins these genes encode may stimulate the autoimmune symptoms of the disease.”

Very interesting! Hopefully this new study can help researchers in getting closer to a cure for rheumatoid arthritis.