What Causes MS?

The cause of MS is not known. Scientists believe MS is triggered by a combination of factors. To identify the cause, research is ongoing in areas of immunology (the study of the body’s immune system), epidemiology (the study of disease patterns in large groups of people) and genetics (understanding the genes that may not be functioning correctly in people who develop MS). Scientists are also studying infectious agents that may play a role.

Understanding what causes MS will speed the process of finding more effective ways to treat it and — ultimately — cure it, or even prevent it from occurring in the first place.

In MS, an abnormal immune-mediated response causes inflammation and damage to the myelin coating that is wrapped around nerve fibers (axons) in the central nervous system (CNS). Also damaged are the cells that make myelin and the nerve fibers themselves. In recent years, researchers have been able to identify immune cells that target the CNS in people with MS, some of the factors that cause them to respond abnormally, and the process of the immune system response. Ongoing efforts to learn more about the immune-mediated process in MS — what sets it in motion, and how to slow or stop it — will bring us closer to understanding the cause of MS.

Although the cause of MS is not known, more is being learned about environmental factors that contribute to the risk of developing MS.  There is no single risk factor that provokes MS, but several factors are believed to contribute to the overall risk.

Geographic gradient
MS is known to occur more frequently in areas that are farther from the equator. Epidemiologists — scientists who study disease patterns in large groups of people— are looking at variations in geography, demographics (age, gender and ethnic background), genetics, infectious causes and migration patterns in an effort to understand why.

Studies have shown that people born in an area with a high risk of MS who then move — or migrate — to an area with a lower risk before the age of 15 assume the risk of their new area. Such data suggest that exposure to some environmental agent before puberty may predispose a person to develop MS later on.

MS “clusters” — the perception that very high numbers of cases of MS have occurred in a specific time period or location — may provide clues to environmental or genetic risk for the disease. So far, cluster studies in MS have not produced clear evidence for the existence of any causative or triggering factor or factors in MS.

Vitamin D
Growing evidence suggests that vitamin D plays an important role in MS. Low vitamin D levels in the blood have been identified as a risk factor for the development of MS.  Some researchers believe that sun exposure (the natural source of Vitamin D) may help to explain the north-south distribution of MS. People who live closer to the equator are exposed to greater amounts of sunlight year-round. As a result, they tend to have higher levels of naturally-produced vitamin D, which is thought to support immune function and may help protect against immune-mediated diseases like MS.

Smoking
The evidence is also growing that smoking plays an important role in MS. Studies have shown that smoking increases a person’s risk of developing MS and is associated with more severe disease and more rapid disease progression. Fortunately, the evidence also suggests that stopping smoking — whether before or after the onset of MS — is associated with a slower progression of disability.

Obesity
Several studies have shown that obesity in childhood and adolescence, particularly in girls, increased the risk of later developing MS. Other studies have shown that obesity in early adulthood may also contribute to an increased of developing MS.  Also, obesity may contribute to inflammation and more MS activity in those already diagnosed with MS.

Many viruses and bacteria — including measles, canine distemper, human herpes virus-6, Epstein-Barr virus (EBV), and Chlamydia pneumonia — have been or are being investigated to determine if they are involved in the development of MS.  EBV, the virus that causes mononucleosis, has received significant attention in recent years. A growing number of research findings indicate that previous infection with EBV contributes to the risk of developing MS.

MS is not an inherited disease, meaning it is not a disease that is passed down from generation to generation.  However, in MS there is genetic risk that may be inherited. In the general population, the risk of developing MS is about 1 in 750 - 1000. In identical twins, if one twin has MS the risk that the other twin will develop MS is about 1 in 4. The risk of developing MS is also increased when other first degree relative (parents, siblings and children) have MS, but far less than in identical twins.

About 200 genes have been identified that each contribute a small amount to the overall risk of developing MS. Research is ongoing to better understand genetic risk and other factors that contribute to the development of MS.