Multiple sclerosis is a disease that may affect any area of the nervous system, thus causing a wide variety of symptoms such as visual problems, weakness, or numbness. Although the exact cause is unknown, it is thought to be an inflammatory process that attacks a substance in the nervous system called myelin. Myelin is the material that surrounds neurons (the cells of the nervous system). Myelin acts to facilitate the rapid transmission of signals up and down neurons, much like insulation around electrical wiring. When the myelin is broken down, the nerve impulses do not travel as efficiently, causing the symptoms that are characteristic of MS.
Who gets MS?
There are approximately 350,000 people in the U.S. and 2.5 million people worldwide with MS. MS typically affects young people. It most commonly starts between the ages of 20 and 40, although less commonly, it can occur later. It affects women more often than men, by a ratio of nearly two to one. People living in the northern latitudes have an increased risk over those living in the southern hemisphere. This suggests an environmental trigger. People who change geographic locations prior to the age of 15 acquire the risk of the region they move to. Although it is not directly inherited, there is some genetic predisposition; there is a one- to three-percent risk of developing MS if a parent or sibling has the disease. Identical twins of a person who has MS have a 25-percent chance of getting the disease. The theory is that there is a genetic predisposition that may be triggered by environmental influences, although we still lack a clear explanation. It is thought that there may be a virus that ultimately acts to trigger the inflammatory or immune response that results in myelin destruction. The main concept is that the immune system recognizes a part of the virus that is similar to that of myelin. Although a number of viruses have been implicated, none have been proven with certainty to be the triggering cause of MS.
