Ancient DNA From Eurasian Herders Sheds Light on the Origins of Multiple Sclerosis

More than 1.8 million people around the world have the autoimmune disease multiple sclerosis (MS). The condition, in which a person’s immune system attacks their brain and spinal cord, is most common in northern Europe, but researchers haven’t been entirely sure why.

A new study of ancient DNA, published Wednesday in the journal Nature, sheds light on this trend, suggesting herders who migrated to Europe from western Eurasia around 5,000 years ago carried genetic variants linked to MS. These variants grew in prevalence at the time and contribute to an increased risk for the disease today, the paper authors write.

“This is a tour de force,” Lluís Quintana-Murci, a population geneticist at the Pasteur Institute in Paris who did not contribute to the findings, tells Nature News’ Sara Reardon.

The study accompanies three other new papers in Nature investigating ancient DNA in Europe and Asia. One of those found that genes linked to an increased risk for diabetes and Alzheimer’s disease were carried by hunter-gatherers.

“Processes that were occurring many thousands of years ago are having these really pronounced and profound effects on the health and longevity of people in the present,” Evan Irving-Pease, an author of all four of the studies and a population geneticist at the University of Copenhagen in Denmark, tells the Washington Post’s Carolyn Y. Johnson.

Researchers explored this history by sequencing ancient genomes and comparing them to modern DNA. The team examined ancient DNA from bones and teeth dating to the Mesolithic period and Bronze Age, as well as new genomes collected from Medieval times. They studied this data against DNA from 410,000 white British people included in the modern U.K. Biobank.

Major migrations had a strong impact on genetic diversity in western Eurasia, the authors write. Hunter-gatherers entered the picture around 45,000 years ago, farmers came from the Middle East around 11,000 years ago and herders migrated from the Pontic Steppe, a grassland region in the Balkans and western Asia, around 5,000 years ago.

These herders, known as the Yamnaya, rode horses and drove ox-drawn carts, writes Science News’ Bruce Bower. And they buried their dead with gold and jewelry, per the New York Times’ Carl Zimmer. Most people in northern Europe today can trace their ancestry to this group.

The researchers found that variants linked to MS arose around 5,000 years ago in the Yamnaya, who spread their genes when they got to northern Europe. These variants increased in prevalence for the steppe population, and later, in the European population, which signaled to the scientists that that they might have provided an evolutionary advantage.

“These variants that are causing the high risk of multiple sclerosis today must in the past have had a benefit,” Eske Willerslev, a geneticist at the University of Copenhagen and a leader of the research, tells the New York Times.

Such variants could have helped ancient people fight off pathogens, the researchers theorize. The overly active immune system associated with multiple sclerosis could have actually been beneficial for surviving plagues, Willerslev tells Nature News. In particular, the MS-associated variants could have protected the Yamnaya herders against diseases carried by their horses, sheep, cattle and goats.

“The situation today is different, because the diseases these variants originally provided protection against are no longer as big a problem as they likely were then,” Lars Fugger, a co-author on the MS paper who studies the disease at the University of Oxford in the U.K., said at a news briefing, per Medpage Today’s Judy George. “Because in the intervening millennia, we have antibiotics, vaccinations and far, far higher standards of hygiene than people had thousands of years ago. The risk genes are now miscast in terms of their original biological role.”

Previous studies have found a couple hundred common genetic variants that are linked to MS, and 30 percent of the risk for the disease is thought to come from genetic factors, the study authors write.

Samira Asgari, a computational biologist at the Icahn School of Medicine at Mount Sinai who was not involved in the research, tells the Washington Post the theory that the variants identified in the study protect against infection is reasonable. But she notes that it’s still a hypothesis.

“That’s the part more research is needed to prove,” Asgari tells the publication.

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.