Multiple sclerosis - Wikipedia, the free encyclopedia

MS occurs mainly in Caucasians. It is twentyfold lower in the Inuit people of Canada than in other Canadians living in the same region. It is also rare in the Native American tribes of North America, Australian Aborigines and the Māori of New Zealand. Scotland appears to have the highest rate of MS in the world.^[45] The reasons for this are unknown. These few examples point out that either genetic background or lifestyle and cultural factors play an important role in the development of MS.

As observed in many autoimmune disorders, MS is more common in females than males; the mean sex ratio is about two females for every male. In children (who rarely develop MS) the sex ratio may reach three females for each male. In people over age fifty, MS affects males and females equally. Onset of symptoms usually occurs between fifteen to forty years of age, rarely before age fifteen or after age sixty.

As previously discussed, there is a genetic component to MS. On average one of every 25 siblings of individuals with MS will also develop MS. Almost half of the identical twins of MS-affected individuals will develop MS, but only one of twenty fraternal twins. If one parent is affected by MS, each child has a risk of only about one in forty of developing MS later in life.^[46]

Finally, it is important to remark that advances in the study of related diseases have shown that some cases formerly considered MS are not MS at all. In fact, all the studies before 2004 can be affected by the impossibility to distinguish MS and Devic's disease (NMO) reliably before this date. The error can be important in some areas, and is considered to be 30% in Japan.^[47]

http://en.wikipedia.org/wiki/Multiple_sclerosis