ST. PAUL, MN -- March 23, 1998 -- A new study helps determine the risk of developing multiple sclerosis (MS) for siblings of MS patients. The study is published in this month’s issue of Neurology.

Factors affecting the sibling risk include: the age of the patient when symptoms began; the sex of the sibling; and whether one of the parents had MS.

The study shows that the younger a patient is when symptoms begin, the more likely it is that a sibling will also develop the disease. Siblings of people who developed MS at age 20 or younger were almost five times more likely to develop MS than siblings of those who developed the disease over 40.

"Despite these increased risks, the actual lifetime risk figures are still low -- well under five percent -- for these siblings," said study author Dessa Sadovnick, PhD, professor of medical genetics at the University of British Columbia.

The study also found that sisters of MS patients are 2.5 times more likely to develop the disease than brothers. Siblings of an MS patient who also have one parent with MS are four times more likely to develop the disease than in families where neither parent has the disease. Again, Sadovnick said, the actual lifetime risk figures are low for both groups.

The study involved 1,896 MS patients in Vancouver, B.C., and 8,878 of their parents and siblings. These findings are important for genetic counseling, Sadovnick said.

"This can help make the answers more specific when patients and family members are asking about the risks," she said. "It's important to have information on the family structure, because it can have an impact on the actual risk for an individual."

The sex of the MS patient has no effect on whether siblings are likely to develop the disease, according to the study.

Researchers believe that a combination of genetic and environmental factors contribute to the disease. The study suggests that those with a greater genetic susceptibility to the disease develop symptoms at a younger age.

Researchers are working on identifying the exact genetic material that causes a susceptibility to MS, Sadovnick said, but have a long way to go. "Hopefully down the road we'll be able to identify people who are at higher risk for developing MS and we can do early interventions to delay or prevent the disease," she said.

About 300,000 people in the United States have MS.

  This material is provided as general medical information and is not intended as advice for individual patients; please contact your physician for specific recommendations.