In the lead up to World MS Day on the 30th of May, I thought I would go through one of the first and most common questions I am asked when I tell someone I have multiple sclerosis; “What causes MS?” or “How did you get MS?” I think this question comes from two places; first, people don’t know much about multiple sclerosis so want to learn more. Second, I think people want to know if it could happen to them. When I was first diagnosed those why my questions, what caused it, why did I get it? It’s a fair question, but it’s a hard question to answer.
The exact cause of multiple sclerosis remains unknown. However, there are four areas of intense research that scientists believe contribute to the development of the disease. It is thought that some combination of these areas triggers MS to develop in some people whilst not in others. These areas are;
The immune system
In multiple sclerosis your immune system doesn’t behave as it should. Ordinarily, the immune system is the body’s defense against infections. When the body senses foreign substances (antigens), the immune system will recognise and eliminate them. As we grow and are exposed to more antigens or we are vaccinated our immune system keeps somewhat of a record of all the antigens it has encountered and defeated so it can recognise and destroy them quickly.
White blood cells play an important role in this immune response. They are involved in the memory of past antigens, they “patrol” the body looking for antigens in our blood and tissues and they trigger the response to attack. What is important to note is that the white blood cells are kept out of the tissues of our central nervous system by the blood-brain barrier. This is to prevent any potential antigens present in our blood from gaining access to our brains, keep this in mind as you read on.
Multiple sclerosis is an immune-mediated disease whereby the immune system malfunctions and attacks the central nervous system, our brains, spinal cord, and optic nerves, causing inflammation and permanent damage. It’s known that the myelin sheath of our neurons are directly affected, but it’s unclear what triggers this attack, i.e. why our own immune system identifies the myelin in our central nervous system as a foreign substance and attacks it.
The white blood cells that are patrolling the body, and ordinarily kept out of our central nervous system somehow manage to cross the blood-brain barrier and enter our central nervous system. They mistake our protective myelin for foreign substances and attack, creating areas of inflammation and can be damaged beyond repair leading to varying levels of disability (these areas of activity are called lesions).
Whilst the process of how the white blood cells are able to cross, or what it is about the myelin that triggers the attacks is unknown, researchers are continuing to investigate this process which may one day lead to a cure but for now results in better therapies and an understanding of the cause of MS.
Multiple sclerosis is not an inherited disease. This means that it is not passed down from generation to generation, unlike diseases such as sickle cell anemia, or cystic fibrosis, however there is a genetic risk that may be inherited. Seeing as you share more genes in common with close relatives such as parents or siblings, those individuals have an overall higher risk than the general population of developing MS if you have it. To put some statistics on it, in the United States the average person has a 0.1% chance of developing MS, but if one parent or sibling has MS that chance jumps to between 2.5 to 5%.
Research has identified about 200 genes that each contribute a little bit to the overall risk of developing MS. We have between 20,000 and 25,000 genes each and of those only about 1% of them differ between 2 individual people – we have a lot in common. People who develop MS are thought to be born with that genetic risk, a susceptibility that some of the 200 of our 20,000 genes have that at some point in our lives is triggered to begin the malfunction of our immune system. The expression of our genes is influenced by our environment, so it could be entirely possible that one person with a genetic susceptibility need only be exposed to certain environmental conditions, or to an infectious agent, and that triggers the development of MS for that individual.
If scientists can understand the genes involved, what makes them susceptible, and what to avoid to prevent MS from developing, we can begin to have more control over a disease that has too much control over some individuals.
There is no single risk factor that triggers the development of MS, but there are patterns, there are factors that scientists believe contribute to your overall risk. Whilst that risk may be quite low for the general population, if you have a close relative with MS knowing these environmental factors and changing behaviours around them could further decrease your potential risk.
Multiple sclerosis is more common the further away from the equator you live. Interestingly, if you live in an area with a high risk of MS, i.e. you live far from the equator, but you move closer to the equator before you turn 15 you assume the risk of the new location. This is incredible, and suggests something about exposure to some environmental agent or infection before puberty may increase your susceptibility to develop MS later on.
When I got diagnosed with MS the first thing my neurologist said to do was to take a vitamin D supplement. There is growing evidence that there is a link between vitamin D and MS. Low vitamin D levels in the blood have been identified as a risk factor in the development of MS, which may also help explain the geographical distributions; MS is higher in countries further from the equator which would be exposed to less sunlight (the natural source of vitamin D). Vitamin D is important as it supports immune function so higher levels of vitamin D may protect against immune-mediated diseases like MS.
Factors far more in our immediate control that contribute to MS are smoking and obesity. Smoking is known to play an important casual role in MS, increasing not only the risk of developing MS, but the severity and speed of disease progression. Studies on obesity in childhood, adolescence, and early adulthood have shown an increase to the risk of developing MS, in some studies by up to 40%. Obesity itself increases overall inflammation in the body and may worsen the immune system activity on the central nervous system of those who already have MS. Thankfully, you can quit smoking and manage your weight, both of which can better your outcome even after diagnosis.
It is possible that bacteria and viruses may have a role in the causation of MS, and as such this is an area of much interest. Research over the last few years has shown that previous infection with the Epstein-Barr virus (glandular fever) can double the population level risk of developing MS. It is also known that viruses cause inflammation and breakdown myelin, so it is entirely possible that exposure to a virus may trigger MS.
Another possibility is that a bacteria or virus that we had been exposed to had similar components to the cells of our central nervous system. When the white blood cells crossed the blood-brain barrier they mistakenly identify our normal healthy brain cells as this virus or bacteria they fought before and begin an attack.
Other factors that contribute to your chances of developing MS include;
- Gender – women are up to 3 times more likely to develop relapsing-remitting MS than men.
- Age – RRMS usually affects those between 20 and 50.
- Ethnicity – people of Northern European descent have a higher risk, but work in 2013 on individuals with MS of non-European ancestry showed that African American women had a higher than previously reported risk of developing MS. This suggests a complex interaction of our genes in the development of MS.
It is clear that multiple sclerosis is triggered by a potential suite of environmental factors in individuals with complex genetic-risk profiles. Taking this into consideration, it’s easy to look through the list and try to pinpoint where I went wrong, what made me get MS, what could I have done differently had I known; but everything is easier with hindsight. This is a futile exercise, and though I can’t really answer the question of “how did I get MS?”, I can answer the question of “what can you do to lower your chances of developing any health condition including MS?” and “what can I do to improve my outcome”. The answer to that question is simple and one that will benefit you across your life; eat healthy, exercise, maintain a healthy weight and lifestyle, and get outside and get some sun.