2023-05-31 14:13:52
Prevalence studies among migrants going from an area of low prevalence of the disease to an area of high prevalence, and vice versa, theoretically make it possible to measure the influence of environmental factors on the risk of developing the disease, but also to indicate in which age group these factors might intervene.2
This work shows that migration before the age of 15 from high-risk regions to low-risk regions reduces the overall risk of MS. Conversely, the risk of MS increases in subjects migrating before the age of 15 from a low risk area to a high risk area; this effect joins the risk of the host region in the second generation.
In addition, studies carried out among natives of the French West Indies migrating to mainland France and returning to their region of origin show that a length of stay greater than 10 years in a high prevalence area (mainland) is necessary to acquire the risk of the host region.
These data highlight the fact that environmental factors acquired in childhood and adolescence play an important causal role in the development of multiple sclerosis.3,4
Two recent studies have made it possible to go even further in the precision of the determinism of MS according to the age of exposure to environmental factors. In the first study, carried out in Denmark (high prevalence area), a link was shown between vitamin D levels in the neonatal period and the later risk of developing the diseaseunderlining the importance of acting very early on this environmental factor that is theoretically easy to correct.5 In the second study, conducted in New Zealand, the effect of latitude gradient on later risk of developing MS was evident from birth, declining following age 12, once more highlighting the early influence of exposure to certain environmental factors.6
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#Multiple #sclerosis #clearer
