What causes MS?

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Much effort and research has gone into finding out what causes MS. However, there are still no clear answers. To the best of our knowledge, the etiology (cause of a disease) of MS seems to involve a combination of factors that working together cause MS. These factors include immunology (functioning of the immune system), environment (different things we are exposed to including where we live), and genetics (our genes).  A more detailed discussion of these factors follows this section.

 

What role does the immune system play in MS? 

Most experts believe that MS is an autoimmune disease, a condition in which the body’s immune system, that part of the body that normally fights invasion by bacteria or other foreign organisms or substances, turns against itself.

In MS, a person’s immune system attacks the central nervous system (CNS), which includes the brain, spinal cord, and optic nerve, causing inflammation that damages myelin, the fatty coating that insulates and protects nerve fibers.

It is not known exactly what antigen (or perceived foreign invader) our immune system is reacting to which causes the inflammatory attack on our CNS.

During an MS relapse or attack, immune cells that normally circulate harmlessly in your blood stream (until your body needs to fight invasion by some foreign substance or organism) attack and breakdown the blood-brain barrier (BBB).

The immune cells, of which there are many different types (T-cells, B-cells, antibodies, cytokines, chemokines) break through the BBB and cause inflammation that destroys the protective covering of nerve cells called myelin, exposing the nerve fiber or axon. Demyelination occurs when inflammation damages the myelin sheath covering the nerve cells.

Once demyelination occurs, the axon (nerve fiber) is exposed and can be damaged by inflammation. In places of demyelination, astrocytes (a type of nervous system cell) help to form scar tissue (sclerosis). In some places where the nerve fiber or axon is exposed, inflammation can lead to a complete break in the nerve fiber resulting in axonal loss.

Myelin functions as insulation around the nerve fiber, like the plastic covering on an electrical wire, and helps nerve impulses travel along the nerve fiber. When demyelination occurs, impulses or signals that normally travel along nerve fibers are slowed or interrupted. This leads to a loss of  communication between the CNS and various parts of the body, resulting in the symptoms associated with MS.