Ancient pastoralists may be responsible for the prevalence of multiple sclerosis in the modern world, scientists have found.

Multiple sclerosis (MS) is an autoimmune disease of the brain and spinal cord that affects 2.8 million people worldwide, according to the National Multiple Sclerosis Society. The United States accounts for roughly one-third of these cases, with a similar percentage originating from Western Europe. But exactly why these countries are so vulnerable to MS has so far remained a mystery—as has the cause of the condition.

Research is ongoing in this area, but scientists believe it to be a combination of genetic and environmental factors, as well as infection history. What we do know is that this combination of factors results in the immune system attacking the fatty insulation that surrounds our nerves in the brain and spinal cord, disrupting their ability to transmit insulation to the rest of the body.

Previous studies have identified 233 genetic variants that are commonly associated with the condition, which experts believe explains approximately 30 percent of an individual’s overall risk of developing the disease. European genetic ancestry has been put forward as a potential explanation for why MS is so prevalent in North America and Europe. But how could these genetic risk factors have promoted the survival of these ancient ancestors?

To explore this evolutionary history, researchers from around the world have come together to analyze ancient genetic data and compare it to modern-day DNA. Their study includes data from nearly 5,000 humans in Europe and Asia, dating back as far as 34,000 years ago.

From their analysis, published in the journal Nature, the researchers found that the genetic variants associated with MS were introduced to European populations around 5,000 years ago by sheep and cattle herders migrating from the East.

“We argue that mutations increasing the risk of MS were favored in Europe thousands of years ago when the pathogenic environment was very different from what it is today,” Rasmus Nielsen, a professor of genetics and evolution at UC Berkeley and a co-author of the study, told Newsweek. “These mutations likely provided protection against pathogens that were common in past environments.”

Specifically, the team believes that these genetic variants may have provided a survival advantage by protecting these herders from infections passed over by their sheep and cattle. Many of these genetic variants appear to play a role in our immune response, which, while making us less susceptible to infections, may also increase our likelihood of developing autoimmune conditions like MS.

“In the context of a modern environment, these genetic variants might cause our immune system to be over-active resulting in autoimmune diseases,” Nielsen said.

William Barrie, another of the study’s co-authors at the University of Cambridge, said: “These results astounded us all. They provide a huge leap forward in our understanding of the evolution of MS and other autoimmune diseases. Showing how the lifestyles of our ancestors impacted modern disease risk just highlights how much we are the recipients of ancient immune systems in a modern world.”

The team hopes that their findings will help us better understand the geographical distribution of this condition as well as its causes.

“These findings help us understand why some of these diseases are so common today,” Nielsen said. “We are a product of the evolution that happened in past environments, and in many ways, we are not optimally adapted to the environment we have created for ourselves today.”

Eske Willerslev, the project’s director and a professor at the Universities of Cambridge and Copenhagen and a Fellow of St John’s College, said that their results also have implications for the way the disease is treated.

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Source: newsweek.com