The presence of shared epitope (SE) genes is the major genetic risk factor so far defined for rheumatoid arthritis (RA). The results indicate that smoking significantly increases the risk of RA among men and women with a genetic predisposition for the disease.
Conducted by a research team in Sweden, this population-based study focused on a large sample of patients with a confirmed diagnosis of the disease - 612 women and 246 men with an average age of 49 years. The researchers also recruited 1,048 healthy individuals to serve as controls. Since former smokers tend to have a wide variation in their cumulative smoking history, the researchers chose to restrict their analysis to current smokers and men and women who had never smoked.
The DNA samples of the RA patients were studied for evidence of SE genes, while the blood samples were tested for rheumatoid factor - a hallmark of one of the subgroup of the disease. Then, the researchers compared current smokers with never smokers for the risk of rheumatoid factor positive RA.
For never smokers with the SE gene, the increased risk for RA was assessed at 2.8 times. For current cigarette smokers without the SE gene, the risk factor was comparable. These findings affirm the SE gene and smoking as independently related to the development of rheumatoid factor positive RA. Among current smokers with the SE gene, however, the disease risk increased to 7.5 times. "The interaction was even more pronounced in smoking subjects with double SE genes, whose relative risk of rheumatoid factor positive RA was 15.7 times higher,” observes one of the authors.
This study has important implications for ongoing research into the factors contributing to RA and other autoimmune diseases, the authors note. "Our study also emphasizes the need to include data on environmental exposures in genetic analyses of a complex disease.”
MEDICA.de; Source: Karolinska Institutet Stockholm