The genetic predisposition to suffer from multiple sclerosis (MS) is closely related to historical migration patterns and the lifestyle of our ancestors. Specifically, MS is linked to genetic contributions made by nomadic populations that arrived in Western Europe 5000 years ago from the Siberian Steppe.
Human genomes vary by 0.1%, and this variation is often the result of responses to environmental pressures. When faced with epidemic disease, for example, natural selection means that the genetic variants that provide individual resistance to pathogens are the ones that survive. These markers, in terms of population genetics, are positively selected.
However, variants that are beneficial in one situation may be counterproductive in another. Immune systems, the first line of defense against harmful viruses and bacteria, tend to become involved in such a mismatch between genetics and environment.
In some cases, immune systems are unable to distinguish between the body’s own cells and foreign ones, causing them to destroy tissue. This is what causes autoimmune diseases such as rheumatoid arthritis, lupus or MS.
In the case of MS, the immune system attacks the insulating coverings of nerve fibers in the brain and spinal cord. Until recently, the cause of MS was unknown, as were the causes of the different distributions among the world’s population. However, new hypotheses have been proposed that may shed light on these mysteries.
MS is more common in Northern Europe
Two sources of information can help us understand when, where, and how MS started. The first is the prevalence of the disease across continental Europe: there are higher concentrations of MS in the north and lower in the south. The second comes from paleogenomics, the study of DNA recovered from ancient remains. Research in this area suggests that the European gene pool consists of three main lineages.
Read more: Early humans reached northwestern Europe 45,000 years ago, new study shows
The basis of the European genome is linked to the first European settlers: hunter-gatherers who arrived in Western Europe about 45,000 years ago. Later, between 8,000 and 6,000 years ago, Neolithic populations from Anatolia migrated into the region, mixing with the hunter-gatherer genome. These groups were associated with the domestication of plants and animals.
Dmitry Butyvsky/Wikimedia CommonsCC BY-SA
To these two previous genomes we can add the Yamnaya migration. The Yamnaya consisted of herding groups from the Pontic Steppes of Siberia, who dispersed throughout Eurasia in the Bronze Age about 5,000 years ago.
Europeans are therefore a complex mixture in varying proportions of these three gene sets.
the nomadic ancestors
A recent study based on ancient DNA analysis has found a direct link between the genetic risk of developing MS and a proportion of individuals of Yamnaya descent. Like the incidence of MS, the Yamnaya genome is more prevalent in northern than in southern Europe.
The contribution of these nomadic pastoralists to European cultural and genetic ancestry had been overlooked by archaeologists until paleogeneticists discovered traces of them in Bronze Age populations.
They were hierarchical, patrilineal, and patriarchal groups who introduced to Europe, among other innovations, the domestication of horses, the use of chariots, and Indo-European languages.
Read more: Indo-European languages: new study reconciles two prevailing hypotheses about their origins
Their arrival in Western Europe also brought the contribution of new genetic variants that were selected to adapt to lifestyles based on animal husbandry and livestock.
YegorGeologist / Wikimedia Commons, CC BY
Coexistence with livestock meant access to milk, a tremendous food source of energy. This in turn led to the selection of genetic variants that allowed adults to properly digest lactose.
Another interesting finding is the presence of some pathogens such as bacteria Yersina pestiswhich causes plague among the remains found by Siberian pastoral groups.
An oversensitive immune system
XVodolazx / Wikimedia Commons, CC BY
Therefore, we can explain the relationship between Yamnaya ancestry and MS, as contact with pathogens carried by cattle caused the Yamnaya’s immune systems to adapt. They became hypersensitive to infections, which sometimes led their immune systems to mistake their own cells for those of others, resulting in the development of autoimmune diseases.
It is perhaps surprising to learn that some characteristics of modern humans, such as the ability to digest lactose as adults, resistance to infectious diseases or the development of autoimmune diseases are inherited from a distant past that developed on the Pontic steppes. This discovery also has potential benefits in the field of medicine, such as the allocation of health care resources to regions with a higher genetic predisposition to developing MS. However, this practical application would require further and more focused research.
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Image Source : theconversation.com