Genes, Environment and Your Arthritis
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Clue 2: All Around You
Your genes don’t tell the whole story. Inheriting a genetic susceptibility to RA does not necessarily mean you will develop the disease.
Studies of identical twins – who have exactly the same set of genes – have shown that when one twin develops RA, the other twin has just a 15 percent chance of developing the condition. So, what environmental factors swing the odds in one direction or the other?
Smoking: Lighting Up Can Set Off Flares
Smoking is the most widely researched environmental factor linked to an increased risk of RA, and researchers recently discovered two specific smoking/gene combinations that can catapult the chances of igniting severe RA.
According to two recent Swedish studies, if a person smokes and has a specific HLA gene for RA, he or she is up to 21 times more likely to develop a more aggressive form of RA, compared with nonsmokers. The more aggressive RA was denoted by the presence of rheumatoid factor in one study and anti-citrulline antibodies in the other.
Researchers do not fully understand exactly how smoking elevates RA risk, but one theory is that the toxins from cigarette smoke – even if secondhand – assault the immune system, increasing the likelihood that RA will develop in those with a genetic predisposition.
The risk of RA has been shown to be highest for women who smoked for the most years, according to a recent study of 103,818 women in the multidecade Nurses’ Health Study. The results suggest, on average, a 49-percent increased risk of RA for current and past smokers compared with nonsmokers, and the risk remained elevated for up to 20 years after the women quit smoking. The researchers leading the study estimate about 25 percent of the new cases of RA in this population may have been prevented if the women never had smoked.
Men who smoke also have an increased risk of RA – perhaps even higher than that for women. Male relatives who developed RA were more likely to have a history of smoking compared with the female relatives with RA, according to a recent study of 467 RA-affected families.
Additional studies have shown smoking also can worsen the severity of RA, increasing the odds of developing RA-related complications, such as vasculitis or inflamed blood vessels.
What the Future Holds
Doctors already counsel patients to avoid smoking. But if physicians have the tools to know who is at highest risk for RA, counseling messages could become more focused and personalized.
“Maybe down the road we’ll be able to screen for RA, especially for people who have it in their families,” says David Felson, MD, chief of the clinical epidemiology research training unit at Boston University School of Medicine, in Boston, and an Arthritis Foundation-funded researcher. “Then we can address the environmental factors, such as smoking, that might ignite the onset,” he says.
