Causes of MS

The overall cause of MS is still unknown. The healthy body's immune system normally defends the body from attack by viruses or bacteria. But in the case of MS, the body's immune system attacks its own myelin, causing disruption to nerve transmission. It is thought that genetic and environmental factors are involved - but the actual trigger to the disease has not yet been discovered.

Symptoms result when inflammation and breakdown occur in myelin, the protective insulation surrounding the nerve fibers of the central nervous system (brain and spinal cord). Myelin is destroyed and replaced by scars of hardened "sclerotic" patches of tissue. Such lesions are called "plaques," and appear in "multiple" places within the central nervous system. This can be compared to a loss of insulating material around an electrical wire, which interferes with the transmission of signals.

The Immune System

It is now generally accepted that MS involves an autoimmune process - an abnormal immune response directed against the central nervous system (CNS). The exact antigen - the target the immune cells are sensitized to attack - remains unknown. In recent years, however, researchers have been able to identify which immune cells are mounting the attack, how they are activated to attack and some of the sites, or receptors, on the attacking cells that appear to be attracted to the myelin to begin the destructive process. The destruction of myelin - the fatty sheath that surrounds and insulates the nerve fibers - causes the nerve impulses to be slowed or halted and produces the symptoms of MS. Researchers are looking for highly specific immune modulating therapies to stop this abnormal immune response without harming normal immune cells.

Environmental Factors

Migration patterns and epidemiologic studies - those that take into account variations in geography, socioeconomics, genetics and other factors - have shown that people who are born in an area of the world with a high risk of MS and move to an area with a lower risk, acquire the risk of their new home, if the move occurs before the age of 15 years. Such data suggests that exposure to some environmental agent that occurs before puberty may predispose a person to develop MS later on.

Viral Factors

Since initial exposure to numerous viruses occurs during childhood and since viruses are well recognized as causes of demyelination and inflammation, it is possible that a virus is the triggering factor in MS. More than a dozen viruses including measles, canine distemper and herpes (HHV-6) have been investigated to determine if they are involved in the development of MS, but it has not yet been definitively proven that any one virus triggers MS.

Genetic

While MS is not hereditary, having a first-degree relative such as a parent or sibling with MS increases an individual's risk of developing the disease several-fold above the risk for the general population. There are studies that show there is a higher prevalence of certain genes in populations with high rates of MS. Common genetic factors have also been found in some families where there is more than one person with MS. Some neurologists theorize that MS develops because a person is born with a genetic predisposition to react to some environmental agent, which, upon exposure, triggers an autoimmune response. Sophisticated new techniques for identifying genes may help answer questions about the role of genetics in the development of MS.

Source - NMSS Information Resource Center and Library. Compendium of Multiple Sclerosis Information (CMSI). National Multiple Sclerosis Society