Potential Causes of Multiple Sclerosis

How a Virus, Where You Live, Your Immune System, and Your DNA Are Linked

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No one knows what precisely causes multiple sclerosis (MS). That being said, four main factors have emerged to attempt to explain why some people develop MS and others do not. While each of these factors can explain a piece of the MS puzzle, none can explain everything. These four causes include:

  • the immune system
  • the environment
  • infectious diseases
  • genetics

Immune System and MS

Though no one knows why, most researchers agree that MS is caused by the immune system attacking the body. Specifically, the immune system’s 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.

Environment and MS

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.

In fact, MS occurs more in places farther from the equator. Many researchers believe that vitamin D may be involved in explaining this phenomenon. 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.

Newer research suggests that higher levels of vitamin D may protect a person from developing MS, and even protect a person who already has MS from getting relapses.

There are other environmental factors that scientists have examined as potential MS triggers including:

  • smoking
  • a high salt diet
  • obesity (especially in adolescence)

Infections and MS

Certain 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.

One virus commonly linked to MS is the Epstein-Barr virus—which causes "mono." This is a very common virus that infects the majority of people at some point in their life. Early exposure to the virus may play a role in MS development, but experts simply do not know for sure at this time.

At this time, no infectious disease (virus, bacteria, or fungus) has been found to definitively cause MS.

Your DNA and MS

Researchers believe that certain genetic combinations increase the likelihood of a person developing MS. In fact, scientists have isolated a number of genes that appear to be linked to MS, most located near the genes that are associated with a person's immune system. In addition to developing MS, it's possible that your genes may also predict the type of MS you have, how severe your disease is, and whether you respond well to MS disease-modifying medications.

This being said, it's important to understand that MS is not a "genetic disease"—meaning that there is not a single inherited gene or set of genes that have been found that indicates a person will definitively get MS. Instead, it seems that genes are one factor, among many, that determine a person’s risk for MS.

Your chances of developing MS increases if you have a relative with MS—another clue that genetics plays a role in MS development. Your chances of developing MS are approximately:

  • 1 in 750 if you have no relatives with MS
  • 1 in 50 if you have a parent with MS
  • 1 in 20 if you have a sibling with MS
  • 1 in 4 if your identical twin has MS
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