Published: Thursday, September 27, 2012, 12:01 a.m.

NEW YORK -- A cellular signature seen in the blood of multiple sclerosis patients may help determine their likelihood of relapse, potentially influencing which therapy physicians prescribe, a study found.

Differences in patients' blood cells delineated them into two groups, one with a 40 percent lower risk of relapse, according to research today in the journal Science Translational Medicine. The findings eventually could help doctors determine whether to prescribe a drug such as Biogen Idec Inc.'s Avonex, which is moderately effective with fewer side effects, or its Tysabri, an aggressive therapy with greater safety issues, said Philip De Jager, a neurologist at Harvard Medical School in Boston and a study author.

Relapsing-remitting MS is the most common form of the illness, which affects more than 2.1 million people worldwide and about 400,000 Americans, according to the National Multiple Sclerosis Society. Patients with RRMS get attacks that degrade their neurological function, followed by periods of recovery.

"This study is a very important contribution to developing the kinds of tools that can help the physician personalize treatment," said Timothy Coetzee, chief research officer of the National Multiple Sclerosis Society, in a telephone interview. "The challenge we've faced in MS is that for a physician there isn't a blood test, like for your cholesterol level," to provide information about the disease.

Doctors aim to be able to attack multiple sclerosis similarly to the way cancer is starting to be treated: by identifying the underlying cause of a patient's tumor and selecting a drug tailored to attack it, said Coetzee, whose group is based in New York and Denver.

In MS, being able to determine a patient's likelihood of flare-ups may lead doctors to prescribe a more aggressive treatment earlier, according to De Jager, who is also an MS specialist at Brigham and Women's Hospital in Boston.

"If we had information about trying to predict the course of the disease, that would be very helpful for managing the patient's care," he said in a telephone interview.

The researchers drew on data from a study of the disease out of Brigham and Women's, feeding information from 363 patients' immune cells into a computer program that hunted for similarities. The analysis turned up two groups of patients, designated MS(a) and MS(b), separated by cellular differences and the likelihood of patients experiencing an exacerbation.

Patients in the MS(a) group expressed more genes in T-cell receptor and B-cell receptor pathways, which play roles in the immune system, and certain others, the researchers found. Those were the patients more likely to have an inflammatory event.

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Multiple sclerosis finding may change therapy strategy