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The Causes of Multiple Sclerosis


Updated June 27, 2014

Causes of Multiple Sclerosis:

No one knows what causes multiple sclerosis (MS). Four main theories have emerged to attempt to explain MS. Each of these theories can explain a piece of the MS puzzle, but none explain everything. It is likely that the cause of MS is a complicated interaction of these four theories: the immune system, the environment, infectious diseases and genetics.

The Immune System and MS:

Though no one knows why, most researchers agree that multiple sclerosis (MS) is caused by the immune system attacking the body. Specifically, the immune system’s T-cells attack cells in the brain and spinal cord, damaging the outer sheath (myelin) of nerves. The damage impacts how well those nerves function – the source of MS symptoms and disability. The disease-modifying treatments work by using different mechanisms to prevent the body’s immune system from attacking the nervous system.


People in certain regions and areas have a higher risk for MS than others. By studying people who move from one area to another, researchers have learned that individual risk changes based on location. They have concluded that some exposure in the environment increases the risk for MS.

MS occurs more in places farther from the equator. Some researchers to believe that vitamin D may be involved in MS. Vitamin D is produced by the body when the skin is exposed to sunlight. In regions far from the equator, the atmosphere filters out more of the sun’s rays which decreases vitamin D production in the body.


Viruses are known to cause damage similar to that seen in MS. Some researchers believe that infections may somehow trigger the immune system to attack nerve cells. Basically, the virus (or bacteria) that causes an initial infection “looks” like a nerve cell. The immune system develops T-cells to fight off the virus. Those T-cells remain in your body after the infection is gone and become confused when they “see” a nerve cell, mistaking it for an invader. The result is that your immune system attacks your nervous system.


A person’s chances of developing MS increase if he or she has a relative with MS. Researchers believe that certain genetic combinations increase the likelihood of a person to develop MS. However the increase in risk is not high enough to call MS a “genetic disease.” Instead, it seems that genes are one factor, among many, that determine a person’s risk for MS. Your chances of developing MS are:

  • 1 in 1000 if you have no relatives with MS
  • 1 in 100 if you have a second-degree relative (grandparent, aunt, uncle, etc.) with MS
  • 1 in 40 if you have a parent or sibling with MS
  • 1 in 4 if your identical twin has MS


Multiple Sclerosis: Hope Through Research ; National Institute of Neurological Disorders and Stroke

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