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Two genetic variations are linked to a higher risk of multiple sclerosis, new studies say.

After three decades of work, scientists said Sunday they have identified two human genes that increase the risk of developing multiple sclerosis, illuminating a new road toward a treatment for the debilitating nerve disease.

Two new studies support what experts and patients have suspected: The disease can be inherited and is caused by the body's immune system attacking itself.

By finding the two genetic variations, a Miami co-author of the studies said researchers could try to develop drugs that block the disease before it starts.

"This tells us very clearly where to look," said Margaret Pericak-Vance, genetics director at the University of Miami School of Medicine. "This is going to be a breakthrough and open the door for new pathways and new therapies."

Medicine has had little to offer the nation's 400,000 MS patients. Six drugs on the market only slow MS. Symptoms range from muscle weakness to paralysis.

The disease strips the coating from nerve cells, disrupting their ability to carry signals from the brain. Scientists believe the disease strikes people who have gene defects that make them susceptible to something - possibly viruses, bacteria or heavy metals - that triggers the condition.

The two new studies, published in the New England Journal of Medicine and Nature Genetics, said the disease is associated with faults in genes called interleukin-2 and interleukin-7.

Supported by grants from the National Institutes of Health, researchers from the University of Miami, Vanderbilt University, the University of California at San Francisco, Duke University and the University of Cambridge participated in both studies, which examined more than 10,000 DNA samples from MS patients in the United States and Europe.

The newly identified defects raise the risk of MS by about 20 percent, researchers said.

Information from the Miami Herald was used in this report.

Fast facts

Who is affected

Multiple sclerosis is a common neurological disease that typically strikes between ages 20 and 50, causing a range of ailments from mild muscle weakness to paralysis. It is two to three times more common in women than men, and more prevalent among those of European descent. About 400,000 Americans have multiple sclerosis.