Causes (etiology) of multiple sclerosis
We do not know for certain what causes multiple sclerosis. Scientists believe that a combination of factors trigger the disease. Studies support the opinion that MS is caused when people with the right combination of genes are exposed to some trigger in the environment. Research also suggests that ethnicity and geography play a role.
To identify the cause of MS, research is ongoing in the areas of:
- Immunology (the study of the body’s immune system)
- Epidemiology (the study of disease patterns in large groups of people)
- Genetics (understanding the genes that may not be functioning correctly in people who develop MS)
- Infectious agents (such as viruses)
Understanding what causes MS will speed up the process of finding more effective ways to treat it and — ultimately — cure it. Ideally, we will find a way to prevent MS from occurring in the first place.
In MS, an abnormal immune response causes inflammation and damage in the central nervous system. Many different cells are involved in the abnormal immune response. Two important types of immune cells are T cells and B cells:
- T cells become activated in the lymph system and in MS, enter the central nervous system through blood vessels. Once in the central nervous system, T cells release chemicals that cause inflammation and damage. This results in damage to myelin, nerve fibers and the cells that make myelin. T cells also help activate B cells and call on other immune system cells to participate in the immune attack.
- T regulatory cells, a type of T cell, dampen or turn off inflammation. In MS, T regulatory cells do not function correctly and do not effectively turn off inflammation.
- Cytotoxic or “killer” T cells directly attack and destroy cells bearing certain characteristics.
- B cells become activated with the help of T cells. B cells produce antibodies and stimulate other proteins, and in MS, these cause damage in the central nervous system.
Researchers continue to search for other cells and processes that could be involved in MS. 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 better therapies and ultimately a cure.
Environmental factors of MS
Although the cause of MS is not known, we are learning more about environmental factors that contribute to the risk of developing MS. There is no single risk factor that provokes MS. Several factors are believed to contribute to the overall risk.
Geography and multiple sclerosis
MS is known to occur more frequently in areas 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. For instance, one study shows that access to healthcare in these areas could explain why MS is more prevalent there.
Other studies have shown that people who move before the age of 15 tend to take on the risk level — either higher or lower — of the area they move to. 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.
More studies are needed to confirm all of these theories.
Vitamin D and multiple sclerosis
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.
Studies of vitamin D supplementation for prevention and management of MS are underway. If you have questions about whether you should consider taking supplements, consult your healthcare provider.
Smoking and multiple sclerosis
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 and multiple sclerosis
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 risk of developing MS. Also, obesity may contribute to inflammation and more MS activity (for example, relapses and lesions on MRI) in those already diagnosed with MS.
Many viruses and bacteria — including measles, canine distemper, human herpes virus-6 (HHV-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.
This does not mean that MS is an infectious disease. MS is not an infectious disease, but latent viruses may play a role in triggering MS symptoms and disease activity. The viruses involved with MS — such as EBV and HHV-6 — are infectious but MS itself is not. MS is not directly caused by germs that enter the body and is not passed from one person to another. You cannot get infected with MS.
Is MS genetic or hereditary?
MS is not an inherited disease — it is not passed down from generation to generation. But people can inherit genetic risk. This means that MS is not genetic in the simpler way that black hair or dimples are. In fact, researchers have identified about 200 genes that each contribute a small amount to the overall risk of developing MS.
Studies of twins have contributed to the belief that genes do play some role. In the general population, the risk of developing MS is about 1 in 334. 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 also increases when other first-degree relatives (parents, siblings and children) have MS, but far less than in identical twins.
Research is ongoing to better understand how genetic risk contributes to the development of MS.
Unproven theories about causes of MS
Researchers have investigated many possible causes of MS without turning up evidence of a link. These theories include:
- Environmental allergies
- Exposure to household pets
- Exposure to the heavy metals — mercury (including mercury amalgam tooth fillings), lead or manganese
- Organic (chemical) solvents
Some of these theories surfaced because people experienced their first MS symptoms after being exposed to something new in their environment. The theories were then disproved by scientific study. If you have any questions about your exposure, consult your healthcare provider.