THURSDAY, Oct. 7, 2004 (HealthDayNews) -- Smoking greatly increases the risk of rheumatoid arthritis (RA) among people with a genetic predisposition for the disease, says a Swedish study in the October issue of Arthritis & Rheumatism.
The study included 858 people with RA and 1,048 healthy people. Blood samples for DNA genotyping were collected from all the participants, who also provided information about their lifestyles, including smoking habits.
The RA patients' DNA was examined for the shared epitope (SE) gene encoding protein sequence, a major genetic risk factor for RA. Their blood samples were also tested for rheumatoid factor, a hallmark of RA.
People with the SE gene who smoked had a 7.5 times increased risk of RA, while those with double SE genes who smoked had a 15.7 times increased risk. People with the SE gene who never smoked had a 2.8 increased risk of RA. Smokers without the SE gene had a 2.4 times increased risk of RA.
The study contributes important information to the ongoing research into factors that contribute to RA and other autoimmune diseases, its authors said.
"Our study also emphasizes the need to include data on environmental exposures in genetic analyses of a complex disease," they noted in a prepared statement.
The Arthritis Foundation has more about rheumatoid arthritis.