CHICAGO (Reuters) - After decades of dead ends, scientists have identified two genes that may raise the risk of multiple sclerosis, lending insight into the causes of the debilitating disease.
The findings, released in two medical journals on Sunday, represent the first genes conclusively linked to multiple sclerosis in more than 20 years, experts said.
MS is a disease of the central nervous system that affects about 350,000 people in the United States and more than 2.5 million people globally.
In a large-scale study appearing in an online version of the New England Journal of Medicine, teams of international researchers scanned the entire human genome of more than 12,000 people for MS risk factors.
That study uncovered two new gene suspects, both of which are thought to play a role in autoimmune disease.
Until now, the only genetic link identified with MS was the major histocompatibility complex, or MHC, a large cluster of genes essential to the immune system.
Neither of the newly discovered genes appears to be as instrumental to developing the disease as MHC, but the research is important because it lends insight into other genetic factors that raise a person's risk of multiple sclerosis.
"Having this genetic road map will be of incredible importance in developing new therapies," said Dr. David Hafler of Harvard Medical School, who worked on the genome study.
The role of one of the gene suspects in MS -- a variant of the interleukin-7 or IL-7 receptor -- was confirmed in two papers published online on Sunday in Nature Genetics.
The gene helps control the activity of regulatory T cells, which suppress the activation of the body's immune system.
"This discovery brings us into a whole new pathway that could have a very important role in understanding the fundamental mechanisms that trigger MS," said Dr. Stephen Hauser, professor of neurology at University of California San Francisco, who worked on studies released online in the New England Journal of Medicine and Nature Genetics.
While the studies used different methods, they both pointed the finger at IL-7.
The Nature Genetics study, led by Jonathan Haines of Vanderbilt University Medical Center in Nashville, Tennessee, and Margaret Pericak-Vance of the University of Miami, examined variants in three genes suspected to have a role in the disease. It found variants in IL-7 receptors were consistently more common in MS patients than in healthy people.
Researchers observed a similar association in a separate study in Nature Genetics by Jan Hillert of the Karolinska Institutet in Stockholm and colleagues, who looked at a large collection of people from Denmark, Finland, Norway and Sweden.
The other gene identified by the whole genome scan -- the IL-2 receptor -- has been linked to two other autoimmune diseases: type 1 diabetes and autoimmune thyroid disease.
"The story here is the commonality of autoimmune disease," Hafler said.
Researchers believe both environmental and genetic factors play a role in the development of MS, which attacks and destroys the insulation along nerve fibers.
MS symptoms range from mild muscle weakness to partial or complete paralysis.