Smoking significantly increases the risk of rheumatoid arthritis among men and women with a genetic predisposition for the disease, according to a study reported in the October issue of Arthritis & Rheumatism.
The team of Swedish researchers investigated the interaction of two specific rheumatoid arthritis risk factors: cigarette smoking and the presence of a protein sequence called the shared epitope, the major genetic risk factor for the disease. The shared epitope is found in cell surface molecules that regulate specific immune responses.
The researchers studied 858 rheumatoid arthritis patients whose average age was 49 years as well as 1,048 healthy individuals to serve as controls.
Participants donated blood samples for DNA genotyping. Every participant also completed lifestyle questionnaires, including smoking habits.
The DNA samples of the rheumatoid arthritis patients were studied for evidence of genes for the shared epitope. The blood samples were also tested for rheumatoid factor, a hallmark of this disease. The researchers then compared current smokers with those who had never smoked for their risk of developing rheumatoid arthritis.
People with the shared epitope gene who never smoked had a 2.8 times greater risk of developing rheumatoid arthritis, compared to 2.4 times for current cigarette smokers without the gene. Among current smokers with the gene, however, the disease risk increased to 7.5 times.
Beyond strengthening the case against cigarette smoking as a health hazard, this study has important implications for ongoing research into the factors contributing to rheumatoid arthritis and other autoimmune diseases.
"Our study also emphasizes the need to include data on environmental exposures in genetic analyses of a complex disease," the authors concluded.
