Multiple sclerosis affects women almost twice as frequently as men. Caucasians are more than twice as likely as African-Americans or Hispanics to get the disease. multiple sclerosis occurs mainly in the Caucasian race. It is 20-fold 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, the Australian Aborigine and the Maoris of New Zealand. These few examples point out that the genetic background plays an important role in the development of multiple sclerosis. The disease is relatively rare among those of Asian decent. The disease is more common in temperate climates, like those in the northern United States, Canada and Europe, than in tropical regions. The fact that multiple sclerosis is more prevalent in certain climates leads researchers to speculate that environmental factors play a role in the development of multiple sclerosis. Research in this area has yet to provide conclusive evidence of a direct link between the environment and multiple sclerosis. As observed in many autoimmune disorders, multiple sclerosis is more common in females than males; the mean sex ratio is about two females for every male. In children, who rarely develop multiple sclerosis, the sex ratio may reach three females for each male, whereas multiple sclerosis occurring in the fifth decade more commonly affects males. Onset of symptoms usually occurs between 20 to 40 years of age, rarely below 15 or above 60, although both are possible. Climate, diet, geomagnetism, toxins, sunlight, genetic factors, and infectious diseases have been discussed as possible reasons for these regional differences. It has been postulated that an environmental factor during childhood might play an important role for the development of multiple sclerosis later in life. This was based on several studies in migrants demonstrating that if migration occurs before the age of 15, the migrant acquires his new region's susceptibility to multiple sclerosis. If migration takes place after 15, the migrant keeps the susceptibility of his home country. Overall, on average one of every 25 siblings of an individual with multiple sclerosis will also be afflicted. Up to every second identical twin of a multiple sclerosis-affected person will develop multiple sclerosis, but only one of 20 fraternal twins. If one parent is affected by multiple sclerosis, only about 1 of 40 of his children will develop multiple sclerosis later in life. In conlusion, the risk factors for multiple sclerosis are: female; age 20-40; family history of multiple sclerosis; Caucasians of Anglo-Scandinavian or North Sea ancestry; living in a geographical area with increased incidence of the disease: above the 37th parallel. http://neurology.health-cares.net/multiple-sclerosis-risks.php