Causes of MS

What causes MS?

A substance called myelin protects the nerve fibres in the central nervous system, which helps messages travel quickly and smoothly between the brain and the rest of the body. In MS, the immune system, which normally helps to fight off infections, mistakes myelin for a foreign body and attacks it.  

Researchers do not know what triggers MS, .but it is likely caused by a combination of genetic risk factors and environmental exposures including: EBV, smoking, low vitamin D levels (either due to low ultraviolet (sunlight) exposure or low levels of vitamin D intake in the diet), and childhood or adolescent obesity. 

Genetic factors

MS is not thought to be a hereditary disease. However, the risk of getting MS is higher in relatives of a person with the disease than in the general population, especially in the case of siblings, parents and children. 

MS is not passed directly from parents to their children because is not caused by a single gene, there is only around a two per cent chance of a child developing MS when a parent is affected. 

For identical twins, having the same genetic material does not mean they will both have MS. If one identical twin has MS, the risk of the second twin developing MS during their lifetime is 20 to 30 per cent. This is why researchers agree that MS is not simply a genetic disease.  

Specific genes have been linked with MS. Most are genes that influence the immune system. These are also the genes that seem to contribute more significantly than others to the susceptibility of the disease.  

The search for MS genes is important because their discovery will provide vital information on which biological mechanisms influence the disease. At the moment, genetic tests for MS are not definitive. A person may have a whole group of gene variants that increase MS risk, but they will not develop MS. Therefore, genetic testing for MS is not used in clinics but for research purposes, to improve understanding of the causes of MS and help in the development of new approaches to treatment and prevention. 

Environmental factors

Various environmental factors have been proposed as risk factors for MS.  

MS is more common in people who live further away from the equator. The reason for this is not clear, but decreased sunlight exposure has been linked with a higher risk of MS and there is growing evidence that a lack of vitamin D is linked to increasing prevalence in a range of conditions including MS. As we get most of our vitamin D through exposure to sunlight, low sun exposure and subsequent vitamin D insufficiency has been proposed as one explanation of this effect. This effect may also explain why there is some evidence that season you are born in may also affect the risk of developing MS. 

There is now compelling evidence linking Epstein-Barr virus (EBV) infection with MS risk. Data showing that EBV infection appears to occur before MS onset, makes it highly probable that EBV may be necessary—but not sufficient—to cause MS. The risk of MS is higher in individuals who have had clinical infectious mononucleosis, suggesting that the severity of EBV infection might play a role in this small subgroup of people with MS. 

Exposure to smoking increases the risk of developing MS compared to the general population. People who smoke have a 50 % higher risk of developing MS than those who do not. The risk of developing MS in smokers may be proportional to the number of cigarettes smoked. Scientists refer to this as a ‘dose-dependent effect’. Similarly, studies suggest that the longer you are exposed to passive smoke, the more the risk of developing MS may go up. Tobacco smoke exposure during childhood is associated with MS risk, with children growing up in homes with smokers having an increased risk of MS onset in childhood or in adulthood.