Developments in Brief : Genetic Link to MS Found in Canada

A new Canadian study offers the strongest evidence yet that multiple sclerosis, the great crippler of young adults, has a strong hereditary cause, although researchers still said environmental factors also play an important role.

“There have been a number of studies that have shown a genetic component,” said Dr. Dale McFarlin of the National Institutes of Health. “This really nails down the genetic contribution.”

The study, conducted by researchers at the University Hospital in Ontario and published in the current New England Journal of Medicine, involved 70 victims of multiple sclerosis and their twins.

The study found that nearly 26% of the siblings who were identical twins also had MS and 2.3% of fraternal twins had the disease, making it only slightly higher than the rate among non-twin siblings.

Identical twins come from a single egg and share all their genes. Fraternal twins come from separate eggs and have different genes.

Dr. Byron Waksman of the National Multiple Sclerosis Society said the new study is significant because it is the best designed of its kind.

Although the findings indicate that relatives of multiple sclerosis patients have an increased risk for the disease, the study also shows that environmental factors play an important role, Waksman said.

“This pins down the fact that even if you have all the necessary genes, you don’t necessarily get MS. That’s very reassuring for some people,” Waksman said.

Researchers think that multiple sclerosis patients inherit a susceptibility to the disease but that the disease is triggered by environmental factors, possibly early childhood viral infections such as measles.

Waksman said the study also indicates that more than one gene is probably involved in the disease.

About 250,000 Americans have multiple sclerosis, and 10,000 new cases are diagnosed each year, primarily in people between the ages of 20 and 40. Its symptoms include weakness, numbness, coordination and balance problems, blurred vision and slurred speech. Some patients become severely disabled.

The disease is apparently caused by patients’ immune systems destroying the coating around nerve fibers.