What Causes Multiple Sclerosis?
One of the most common questions that I (understandably) get asked by patients and their families is: What causes multiple sclerosis (MS)? The short answer is that no one knows, and I tell my patients that if I knew the answer to that question, I would be one of the most famous doctors in the country. There are some known risk factors, however.
Genetics play a role in MS, though a small one. If a first-degree relative, such as a sibling or a parent, has the illness, the odds that a person will contract the illness are about three percent. In the United States, the overall risk of developing MS is about one in 750 people. So while the rate of MS for people with affected family members is substantially higher than that of the general population, the overall rate is still very low. Even in identical twins whose share the same DNA, the odds of one twin getting MS if the other has it are only around 30 percent.
Sex matters. As with most autoimmune illnesses, MS affects twice as many women as men. A report from Canada in 2006, shows that this imbalance has become even more pronounced in recent years for reasons that are not clear.
The illness also does not occur equally in all ethnic groups. Caucasians tend to have the highest rate of the illness, while African-Americans have a much lower rate. In black people from Africa, the disease is almost unheard of.
The risk of contracting the illness also depends on where one spends the first 15 years of their lives. People who live near the equator have very low rates of MS, and the rate of MS increases the further one travels away from the equator. The rate of MS in Ohio is almost double that the rate in Texas. There are several theories as to why this might be, but the most likely is that people who live near the equator have higher rates of exposure to UV light, which the body requires to make vitamin D. Low vitamin D levels have been linked to MS.
Exposure to Infectious Agents
Additionally, infectious agents have long been suspected to be a cause of MS. MS was unknown in certain parts of the world until they were colonized by Europeans.
The most evidence exists for infection with the Ebstein-Barr virus, the virus that causes mononucleosis. Although the vast majority of the population has evidence of exposure to the virus, in patients with MS, the rate approaches 100 percent.
Finally, the only behavioral factor that leads to MS is that old demon cigarette smoking, which doubles the risk of developing MS.
So, there is no single cause of MS. Rather, it is an illness that occurs in genetically vulnerable individuals exposed to certain environmental conditions. Certainly much more work remains to be done in this area and more discoveries are on the horizon. Patients with MS can take solace in the fact that, except for not smoking, there is nothing they could have done to prevent the illness.