Multiple Sclerosis - Causes
Multiple sclerosis is an autoimmune disease in which the immune system begins to attack myelin. It "decides" that the myelin is a foreign substance that threatens the body and must be destroyed. Researchers do not know why this happens.
As myelin is destroyed, neurons no longer function normally. Brain neurons cannot receive and process information from the outside world. Neurons in the brain and the spinal cord cannot send messages to other parts of the body. Normal muscular functions, such as standing, walking, lifting, and turning, become difficult or impossible.
The progress of MS seems to depend on the appearance of new plaques. These plaques slow down nerve messages and worsen the symptoms of the disease. Scientists do not understand how, where, and why plaques develop. For that reason, they cannot predict how the disease will progress in any one person over time.
Finding the reason for a body's autoimmune reaction to myelin is a major field of research. So far, no final answer has been found. Some possible factors leading to this condition are a person's heredity (his or her genes), environmental factors, viruses, or a combination of these factors.
The reason that heredity is considered a possible factor is that MS seems to run in some families. A person who has a family member with MS is more likely to develop the disease than someone whose family has no history of MS. In addition, the tendency of some ethnic groups to contract (get) the disease suggests a hereditary factor.
Support for environmental factors comes from data on migration. Migration is the process of moving from one part of the world to another part. Studies have been done on people who move from a low-risk part of the world (such as Asia) to a high-risk part (such as the United States). Young people who make such moves have a higher risk of developing MS than those of the same age who remained at home. Older people do not experience an increased risk. These data suggest that environmental conditions in the new location might be responsible for MS.
One possible environmental factor is viruses. There are some kinds of viruses that attack the body very slowly. HIV, the virus that causes AIDS (see AIDS entry), is one such virus. Some researchers think that a slow-acting virus may be responsible for MS. But no data supporting this theory have yet been produced.