Female smokers or ex-smokers with rheumatoid arthritis, who also lack a particular detoxifying enzyme are more likely than nonsmokers to develop a severe form of the disease, a new study finds.
The GSTM1 gene produces an enzyme that detoxifies carcinogens in tobacco smoke. However, people can be born without this gene, usually depending on their ethnic group. It is more common to find a Caucasian without the gene than an African.
The study, carried out by researchers at the Staffordshire Rheumatology Centre in England, aimed to investigate the effects of smoking on rheumatoid arthritis. It is published in the recent issue of Arthritis & Rheumatism.
Researchers assessed 164 northern European white women with rheumatoid arthritis. Eighty of these had never smoked, 35 were ex-smokers and 49 were smokers.
Using x-rays of joint damage and assessing the participants ' ability to perform everyday tasks, the team found that the disease was worse in patients who were smokers or ex-smokers than in patients who had never smoked.
However in those that lacked the GSTM1 enzyme, the severity of rheumatoid arthritis was significantly greater in smokers and ex-smokers than in nonsmokers. In those with the GSTM1 enzyme, smoking did not have a noticeable effect.
The researchers explained that the difference could be influenced by the body's production of rheumatoid factor, a substance produced by the majority of patients, and considered a marker of the disease.
As in previous studies, the team concluded that current smokers were much more likely to have rheumatoid factor than patients who had never smoked, and the number of years of smoking was also a contributory factor. However they noted that was only relevant in patients without the GSTM1 enzyme.
It is likely that the GSTM1 enzyme detoxifies the damaging chemicals in smoke which would otherwise cause the body to produce more rheumatoid factor.
The team concluded that disease outcome in female RA patients with a history of smoking is significantly worse than in those who have never smoked. Smoking was associated with the most severe disease in patients who did not carry the GSTM1 gene.
Further studies will likely focus on the impact of other genes in the association between smoking and severity of rheumatoid arthritis, and also on other populations with different genetic factors.