Scientists have traced the genetic roots of the auto-immune neurodegenerative disorder called multiple sclerosis (MS) to genes inherited from livestock herders and pastoralists in the eastern Europe and central Asian region more than 5,000 years ago.

A study released on Wednesday has shown that the genetic risk for MS — a disorder influenced by both genes and lifestyle — emerged among pastoralists from the Pontic-Caspian steppe and was brought into Europe by population migrations around 5,000 years ago.

The gene variants that enhanced the risk of MS provided a survival advantage to the livestock herders called the Yamnaya population, likely by protecting them from infections they could catch from their cattle and sheep, according to the study published on Wednesday in the research journal Nature.

“It must have been a distinct advantage for the Yamnaya people to carry the MS risk genes, even after arriving in Europe, despite the fact that these genes increased their risk of MS,” said Eske Willerslev, a Danish evolutionary geneticist at the University of Cambridge in the UK who led the study.

Earlier studies have identified 233 genetic variants that increase the risk of MS by about 30 per cent. In the new study, Willerslev and his colleagues looked for these variants in ancient populations, relying on a genebank from ancient Europeans going back to 34,000 years ago.

They found that the genes linked to MS were also present in bones and teeth from thousands of years ago. “These results astounded us all,” said William Barrie, a post-doctoral researcher at the University of Cambridge and a study co-author.

“They provide a leap in our understanding of the evolution of MS and other auto-immune diseases, showing how the lifestyles of our ancestors impacted modern disease risk just highlights how much we are recipients of ancient immune systems in a modern world,” Barrie said in a media release.

MS is an auto-immune condition involving the brain and spinal cord in which human immune system cells attack the protective insulating sheath around the nerve fibres. The symptoms depend on the site and severity of the nerve fibre damage and range from numbness and tingling to difficulty in walking to fatigue and vision damage, among others.

While the genes that enhanced the risk of MS helped protect the ancient people from possible infections they could catch from cattle or sheep, modern lifestyle choices and improved hygiene have meant that most present-day humans no longer face such infections.

“We now lead very different lives from those of our ancestors — in terms of hygiene, diet, and medical treatment options,” said Astrid Iversen, professor of virology and a study co-author at the University of Oxford. “This combined with our evolutionary history means we may be more susceptible to certain diseases than our ancestors were — including auto-immune diseases such as MS.”