Smoking may enhance link between existing risk factor and muiltiple sclerosis (MS)..

April 9, 2010 - Smoking appears to enhance the link between an existing risk factor and multiple sclerosis, nearly doubling the chances of getting the disabling neurologic disease, according to a new study.

PAPER: Combined effects of smoking, anti-EBNA antibodies, and HLA-DRB1*1501 on multiple sclerosis risk, K. C. Simon ScD*, I. A.F. van der Mei PhD, K. L. Munger ScD, A. Ponsonby MD, PhD, J. Dickinson PhD, T. Dwyer MD, P. Sundström MD, PhD, and A. Ascherio MD, DrPH, Neurology 0: WNL.0b013e3181dad57ev1, ABSTRACT..

The existing risk factor is having high levels of antibodies to the Epstein-Barr virus (EBV), a common herpes virus that infects most people but is associated with multiple sclerosis (MS) in a small fraction of those who have it. Previous research has found a link between high levels of EBV antibodies and the disease, said the study's lead author, Kelly Claire Simon, a research associate at the Harvard School of Public Health.

Simon and her colleagues evaluated 442 people with MS and 865 healthy people without the disease who had been participants in three large studies: The Nurses' Health Study I/Nurses' Health Study II, the Tasmanian MS Study and the Swedish MS Study.

"Having the HLA DR15 risk gene (an immune system-related gene) did not appear to be affected by smoking or not," Simon said. But higher antibody levels of EBV did affect risk in those who had ever smoked, compared to those who had never smoked. "The increasing risk of MS associated with higher EBV antibody [levels] was stronger among ever-smokers than never-smokers," Simon said. Among the participants with higher levels of the EBV antibody, smokers were twice as likely to have MS as those who had never smoked. The association was not seen in those with lower antibody levels, however.

Exactly how the smoking enhances the link between the high antibody levels and MS risk isn't known, the researchers added. Previous research has found those already diagnosed with MS who smoke are at higher risk for getting the brain lesions associated with the disease, and for brain shrinkage.

Overall, a person's lifetime risk of getting MS is one in 200 for women and one in 600 for men in the United States. Those with the higher antibody levels in the study had up to a twofold increase in risk if they smoked, compared to nonsmokers, the Harvard researchers found.

Reference: Smoking May Boost MS Risk in Some by Kathleen Doheny, Health Day Reporter, 4/7/2010.

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