brain, spinal cord, and nerve disorders
Multiple Sclerosis (MS)
Causes of Multiple Sclerosis
The cause of multiple sclerosis is unknown, but a likely explanation is that people are exposed early in life to a virus (possibly a herpesvirus or retrovirus) or some unknown substance that somehow triggers the immune system to attack the body’s own tissues ( Autoimmune Disorders ). The autoimmune reaction results in inflammation, which damages the myelin sheath and the underlying nerve fiber. Genes seem to have a role in multiple sclerosis. For example, having a parent or sibling (brother or sister) with multiple sclerosis increases the risk of acquiring the disease several-fold. Also, multiple sclerosis is more likely to develop in people with certain genetic markers on the surface of their cells. Normally, these markers (called Recognition ) help the body to distinguish self from nonself and thus know which substances to attack. Environment also has a role in multiple sclerosis. Where people spend the first 15 years of life affects their chance of developing multiple sclerosis. It occurs as follows: In about 1 of about 2,000 people who grow up in a temperate climate In only 1 of about 10,000 people who grow up in a tropical climate Much less commonly in people who grow up near the equator These differences may be related tovitamin Dlevels. When the skin is exposed to sunlight, the body formsvitamin D. Thus, people who grow up in temperate climates may have a lowervitamin Dlevel. People with a low level ofvitamin Dare more likely to develop multiple sclerosis. Also, in people who have the disorder and a lowvitamin Dlevel, symptoms appear to occur more frequently and are worse. But howvitamin Dmay protect against the disorder is unknown. Where people live later in life—regardless of the climate—does not change their chances of developing multiple sclerosis. Prior infection with Infectious Mononucleosis (which causes mononucleosis) appears to increase the risk of developing multiple sclerosis. Cigarette smoking also appears to increase the chances of developing multiple sclerosis. The reason is unknown. Spending the first 15 years of life in a temperate (rather than tropical) climate increases the risk of multiple sclerosis. Three fourths of people with multiple sclerosis never need a wheelchair. 