Epidemiology of Multiple Sclerosis

Epidemiology studies have been very common in MS and have led to different theories about the possible causes of the disease. Although MS can also affect children, the majority of cases are diagnosed amongst adults between the age of 20 and 40, with very few cases diagnosed after the age of 60. The primary progressive subtype is more common in people in their fifties. As in most auto-immune conditions, women are more than twice as likely to develop the condition as men.

There is a very specific distribution of this disease in the different parts of the world. A much higher prevalence of the disease is found in the regions most distant from the Equator in both hemispheres, such as Scandinavia, UK, northern European countries, North America, Australia and New Zealand. However, there are some unexplained exceptions in its geographical distribution, such as the high incidence and prevalence of the disease in the Canary Islands. This shows that environmental factors may be significant.

The data from migration studies shows that if migration happens before the age of 15, individuals acquire the susceptibility of the new country, while if the migration happens after the age of 15, they retain that of the country of origin.

Other studies also show differences in susceptibility to MS between different populations. Individuals from the same ethnic group have very similar prevalence rates and show a fewer predisposition to the disease regardless of latitude. There is a low incidence of the disease amongst Lapps in Scandinavia and Native Americans for instance, contrary to their northern location. The condition is uncommon in Asia and almost unknown among the indigenous populations of Africa. White populations are at higher risks than other groups. Researchers have not found an explanation for these distribution patterns yet.