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Familial risk includes both genetic risk factors and non-genetic risk factors that affect members of the same family. These findings were recently published in Arthritis & Rheumatology.

Although family history may contribute to RA, it doesn’t entirely explain an individual’s risk. Many people with a family history of RA will never develop the condition themselves. Similarly, RA may develop in someone with no family history of the condition. In addition to genetic factors, it’s also possible that family members are often exposed to the same environmental risk factors for RA. As a result, it’s hard to know how much of the risk is genetic and how much is due to other factors that affect members of the same family.

To better understand the role of familial risk and the development of RA, researchers in Sweden used national databases to find first-degree relatives with RA. To assess risk factors within these families, they accounted for genes known to play a role in RA as well as for known non-genetic risk factors—such as smoking, alcohol intake, having given birth, exposure to silica (a mineral compound often found in construction materials), body mass index, fatty fish consumption, and education.

The researchers found that the non-genetic risk factors didn’t appear to explain to the risk of RA within families. They did find, however, that known genetic factors did appear responsible for certain cases of RA, but only a small amount.

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These findings suggest that known risk factors for RA (genetic and non-genetic) only played a small role in the development of RA within families. This means that several familial risk factors that have not been identified might still exist. Importantly, family history is still a significant risk factor for RA.

Reference: Jiang X, Frisell T, Askling J, et al. To What Extent Is the Familial Risk of Rheumatoid Arthritis Explained by Established Rheumatoid Arthritis Risk Factors? Arthritis & Rheumatology. 2015 February; 67(2):352-62.