Studies have shown support for the opinion that MS is caused by early exposure to some environmental trigger in genetically susceptible individuals. Research also shows ethnicity and geography
impact the prevalence of MS.
Genetic factors are thought to play a significant role in determining who develops MS.
The average person in the United States has about one in 750 (.1%) chance of developing MS.
For first-degree relatives of a person with MS, such as children, siblings or non-identical twins, the risk rises to approximately 2.5-5% — with the risk being potentially higher in families that have several family members with the disease. The identical twin of someone with MS (who shares all the same genes) has a 25% chance of developing the disease.
If genes were solely responsible for determining who gets MS, an identical twin of someone with MS would have a 100% chance of developing the disease. The fact that the risk is only one in four demonstrates that other factors, including geography and an infectious trigger, are likely involved as well.
Research has demonstrated that MS occurs in most ethnic groups, including African Americans
, Asians and Hispanics/Latinos
, but is most common amongst Caucasians of northern European ancestry.
Susceptibility rates vary among these groups, with recent findings suggesting that African American women have a higher than previously reported risk of developing MS and Hispanic Americans have a higher incidence of MS compared with their ancestral countries of origin.
While MS is generally more common in areas farthest from the equator, MS is almost unheard of in some populations, including the Inuit, Yakutes, Hutterites, Hungarian Romani, Norwegian Lapps, Australian Aborigines and New Zealanders — indicating that ethnicity and geography impact prevalence figures in different parts of the world.
Migration from one geographic area to another seems to alter a person’s risk of developing MS. Studies indicate that immigrants and their descendants tend to take on the risk level — either higher or lower — of the area to which they move. The change in risk, however, may not appear immediately.
Those who move in early childhood tend to take on the new risk themselves. For those who move later in life, the change in risk level may not appear until the next generation.