For the study, researchers screened the oligoadenylate synthetase (OAS1) gene in 401 people with MS, 394 people without MS and 178 people receiving the MS treatment beta interferon.

On the analysis of the OAS1 gene, 63 percent of people with MS had the AA genotype compared to 57 percent of people without MS. The GG genotype was found in 37 percent of people with MS compared to 43 percent of people without the disease.

While the OAS1 gene was weakly associated with disease susceptibility, the study found that people who had the AA genotype had earlier relapses and increased disease activity compared to those without the genotype.

"While we don't understand why some patients vary so widely in their disease activity, this genetic association may give us clues to help direct future research," said study author Margaret O'Brien, PhD, with St. Vincent's University Hospital in Dublin, Ireland.

The study also found people who had the GG genotype had less disease activity and fewer relapses. "It's possible that the GG genotype may protect against increased disease activity in people with MS, but more research is needed," said O'Brien.

The study was supported by Science Foundation Ireland, the Health Research Board of Ireland and MS Ireland.