Multiple sclerosis epidemiology and demographics
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Epidemiology and Demographics
In northern Europe, continental North America, and Australasia, about one of every 1000 citizens suffers from multiple sclerosis, whereas in the Arabian peninsula, Asia, and continental South America, the frequency is much lower. In sub-Saharan Africa, MS is extremely rare. With important exceptions, there is a north-to-south gradient in the northern hemisphere and a south-to-north gradient in the southern hemisphere, with MS being much less common in people living near the equator.[1] Climate, diet, geomagnetism, toxins, sunlight exposure, genetic factors, and infectious diseases have all been discussed as possible reasons for these regional differences. Environmental factors during childhood may play an important role in the development of MS later in life. This idea is based on several studies of migrants showing that if migration occurs before the age of fifteen, the migrant acquires the new region's susceptibility to MS. If migration takes place after age fifteen, the migrant keeps the susceptibility of his home country.[2] However other works suggest that the age/geographical risk for developing multiple sclerosis spans a larger timescale than just the first 15 years of life.[3]
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.[4] 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.[5]
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.[6]
References
- ↑ Epidemiology and multiple sclerosis. a personal review
- ↑ Marrie, RA. Environmental risk factors in multiple sclerosis aetiology. Lancet Neurol. 2004 Dec;3(12):709-18. Review. PMID 15556803
- ↑ Hammond SR, English DR, McLeod JG (2000). "The age-range of risk of developing multiple sclerosis: evidence from a migrant population in Australia". Brain. 123 ( Pt 5): 968–74. PMID 10775541.
- ↑ Rothwell PM, Charlton D (1998). "High incidence and prevalence of multiple sclerosis in south east Scotland: evidence of a genetic predisposition". J. Neurol. Neurosurg. Psychiatr. 64 (6): 730–5. PMID 9647300.
- ↑ Sadovnick, AD, Ebers, GC, Dyment, DA, Risch, NJ. Evidence for genetic basis of multiple sclerosis. The Canadian Collaborative Study Group. Lancet 1996; 347:1728. PMID 8656905
- ↑ Weinshenker B (2005). "Western vs optic-spinal MS: two diseases, one treatment?". Neurology. 64 (4): 594–5. PMID 15728277.