Multiple Sclerosis InfoCenter - Geographic Distribution

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Is Multiple Sclerosis an inherited disease? Is it genetically linked? Is it caused by outside agents, such as viruses? Does exposure to environmental factors play an influencing role? Are some people immune to the disease? These are just a few of the questions researchers have been asking, but have yet to answer definitively. Based on population studies and geographic distribution of MS cases, scientists now believe that the presence of MS is influenced by both genetic factors and environmental exposure.

Age at Onset Multiple Sclerosis is a disease that affects some 2.5 million people worldwide. About 70% of MS patients experience their first symptoms between the ages of 21 and 40. On the average, age at diagnosis peaks near age 27. Onset of the disease prior to age 15 or after age 55 is very rare, although there have been patients diagnosed as young as 3 and as old as 67.

geographical distribution Based on observations, there appears to be a fairly strong statistical correlation between incidence of MS and geographic latitude. In other words, the farther one travels from the earth's equator, the more cases of MS per capita one finds. In particular, Great Britain, Scandinavia and Canada have three of the highest rates of MS in the world. These regions are known as higher risk environments and seem to play an important role in epidemiology.

Of particular interest is one study of the incidence of MS cases among the white population of South Africa, an area considered to be a low risk environment. Incidence of MS in South Africa The study revealed that a significantly higher incidence of MS occurred among those South Africans who had migrated after adolescence from Great Britain, a higher risk environment. Incidence of MS among the native South African whites was much lower. This suggests that individuals assume the risk level of the environment in which they spend their adolescence (up to about age 15).

There have also been population studies that show certain groups of people to be immune, or at least highly resistant, to the disease. MS is all but nonexistent in the equatorial regions of Africa and among the Alaskan Inuit. Lapps in Scandinavia also appear resistant. Native Americans rarely are diagnosed with MS and very few cases are reported in Japan, China and South America. Overall, caucasian people are at a higher risk than either Blacks or Asians.

There have been a number of epidemics of MS reported, the most notable of which occurred in the Faroe Islands during World War Two. A cause or "agent" was never identified, however the epidemic occurred just after the islands had been occupied by British troops.

concordance rate among monozygotic twins Studies of MS among family members suggest there is some genetic influence. According to the data, a person is 20 times more likely to develop MS if a first-degree relative (parent or sibling) has the disease. Among monozygotic (identical) twins in which the disease is present, 30% display a presence in both twins. Among dizygotic (fraternal) twins, the rate drops to 5%.