Multiple sclerosis is an inflammatory demyelinating disease that most often appears in young adulthood, with the incidence peaking around age 30 (Wingerchuk, 2011). It occurs more commonly in women than men (at a ratio of approximately 3:1, although there is some evidence that the ratio may be increasing (Dunn & Steinman, 2013; Trojano et al., 2012; Orton et al., 2006).
MS is common in areas inhabited by people of northern European ancestry. It is more common in Europe, the United States, Canada, New Zealand, and some parts of Australia; it is much less common in Asia and rare in tropical and sub-tropical regions (Compston & Coles, 2008). With some notable exceptions, the global distribution of MS increases with distance north or south of the equator, although there is some evidence that the north-south incidence gradient may have disappeared in the northern hemisphere (Koch-Henriksen & Sorensen, 2011).
MS is an immune-mediated disease that targets the central nervous system. Although MS is thought by some to be autoimmune, the specific antigen(s) have not yet been identified. The cause of MS involves both genetic and environmental factors, with the age at which the interaction occurs playing a key role as well (Compston & Coles, 2008). Migration studies have demonstrated that migration during childhood from a region of high MS prevalence to a region of low prevalence is associated with a reduction in risk, while the reverse is associated with an increase in risk (Dean & Kurtzke, 1971; Alter et al., 1962; Detels et al., 1977).