The genetic predisposition to suffering from multiple sclerosis (MS) is closely linked to historical migration patterns, and to our ancestors’ lifestyles. Specifically, MS is linked to the genetic contributions made by nomadic populations who reached Western Europe 5000 years ago from the Siberian Steppe.
Human genomes vary by 0.1%, and this difference is often the result of responses to environmental pressures. When faced with epidemic diseases, for instance, natural selection means the genetic variants that provide individual resistance to pathogens are the ones that survive. These markers are, in terms of population genetics, “positively selected”.
However, variants that are beneficial in one situation can be counterproductive in another. Immune systems – the first line of defence against harmful viruses and bacteria – tend to be 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 external ones, leading them to destroy tissues. This is what causes autoimmune diseases such as rheumatoid arthritis, lupus or MS.
In the case of MS, the immune system attacks the insulating covers of nerve fibres in the brain and spinal cord.........