Multiple Sclerosis, MS, is a disease causing a range of symptoms including stiffness, partial paralysis and visual problems. It is caused by the patient’s immune system attacking the protective sheath surrounding nerve fibres, resulting in localised nerve damage. The disease often shows episodes of damage followed by slow recovery, or it can be progressive.

Globally around 2.5 million people have MS, but there is high prevalence in Scandinavia and some European countries including Italy and Germany. Here just over 1 in every 1,000 people can be affected.

MS develops in adulthood. The causes are unclear, and probably complex. Environmental factors are undoubtedly significant. For instance the widespread Epstein-Barr virus commonly infects us in childhood where it appears essential harmless. But people who are first infected with it as adults have a 30-fold increased risk of developing MS.  

MS is not a straight-forward genetic disease: it is not inherited. But extensive analysis of the genomes of MS patients identified some 230 gene variants which are associated with the disease. Prominent among these is a variant of the HLA system which is a key component of immune responses. This variant is known by the code name HLA-DRB1*15:01. It is estimated to confer a 3-fold higher risk of MS on those who carry it. This is some 20% of the Northen European population, a much higher proportion than found in southern and western Europe.

So how did this relatively localised abundance of HLA-DRB1*15:01 arise? In a series of 4 papers recently published in the j0urnal Nature, a large international team reported their extensive analyses of the genomes of ancient and medieval skeletons across Europe. This combined with archaeological evidence reveals that Europe was populated by 6 waves of different peoples migrating in from the east. One of these, animal herders from the Steppes, the Yamnaya people, carried the HLA-DRB1*15:01 gene variant. The Yamnaya contributed heavily to the gene pool of Northen Europe and Scandinavia. Moreover the frequency of HLA-DRB1*15:01 in these populations increased in the medieval period, most likely as it offered better resistance to waves of infectious diseases.

The thinking is therefore that the survival advantage of a powerful immune system also carries with it an increased risk of autoimmune diseases such as MS.  

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31st Jan 2024