MS Active Source - positive living with MS

What Causes Multiple Sclerosis?

Despite a great deal of research, what causes MS is still unclear. In general it is thought that MS is an ‘immune-mediated disorder that occurs in genetically susceptible people’ (refM5). In other words, people may develop MS because they have genes that somehow make it more likely that, given a necessary ‘ trigger’, the immune system will start to attack myelin.

So, even though the sequence of events that initiates the disease is largely unknown (refM5), it is known that the following are involved:

• Autoimmune reaction.
• Hereditary factors.
• Environmental factors.

 

Figure: Probable Factors in the Development of MS

 

Autoimmune Reaction

The immune system is designed to protect people from outside enemies, such as viruses or bacteria that cause illness. Factors that cause the immune system to react are known as antigens. If the immune system recognises such an antigen, the first stage in its defence is an inflammatory reaction. This is followed by the production of antibodies and migration of special cells, such as T-cells, to fight off the threat.

Generally, inflammatory reactions occur only when the immune system reacts to antigens, such as viruses and bacteria. But, in some cases, an inflammatory reaction against our own body parts or tissues happens. Diseases in which this process occurs are called ‘autoimmune’ diseases.

It is believed that MS is such an autoimmune disease because, as described earlier, people with MS have inflammatory reactions against the myelin in their own CNS.

More evidence that MS is an autoimmune disease comes from laboratory studies. In these, a condition like MS can be caused in animals by injecting them with brain tissue that activates their immune system. Also, many autoimmune diseases, such as rheumatoid arthritis, lupus, and diabetes, are more common in women than in men; this is also true of MS.

Hereditary Factors

MS does appear to be hereditary, to some extent. Studies of identical twins show that a person has a 33% chance of developing MS if their twin already has it. However, if the cause was solely genetic, the twins' chances of developing MS would be 100%, since identical twins share the same genes. This means that other factors also have to be present.

But it is important to understand that family members of someone with MS do have a higher risk of contracting the disease than people without a family member with MS.

Despite ongoing research, scientists have not yet found the location of the hereditary factors involved in MS. They estimate that more than 20 genes are involved.

More information can be found in the Living with MS section of this site.

Environmental Factors

Geography: MS does not occur as frequently in every country throughout the world. The disease most commonly affects Caucasians, particularly in North America, Europe and Australia (see figure) (refM5). But the differences between people of different races are not as great as was originally thought.

Figure: Incidence of MS by Region

It is known, however, that in both the northern and southern hemispheres MS is more common the farther away a country is from the equator. This applies to regions within a country itself. For example, in the USA, the incidence of MS is much higher in northern states with temperate climates (seasonal changes) than in warmer southern states.

Some studies suggest that there may be a connection between where a person lived for about the first 15 years of his or her life and the incidence of MS (refM5). For example, children up to age 15 years who move to another area where there is a higher or lower risk for MS become as likely to get MS as people who have always lived in the new area. But people older than 15 years who move remain as likely to get MS as people who live in the area where they grew up.

Viruses

Much research has studied the links between MS and all kinds of viruses. As yet there has been no reliable proof of any specific virus being responsible for MS. A likely possibility is that MS is the result of a response to several outside factors, such as viral infections, in a person who may be susceptible to MS based on his or her genetic make up.

Table: Summary of the Possible Development and Initiation of MS

Presence of genetic and environmental factors that make MS more likely

Breach of blood-brain barrier

T-cells and antibodies move into the CNS and attack myelin

Triggering of immune response

If attack predominates over defence, myelin and myelin- producing cells are damaged

Loss of myelin from areas of axons results in only partial insulation of electrical transmission

Transmission of information and instructions is therefore slowed or blocked

Exposed parts of axons without myelin come under further attack

Irreversible axonal injury may occur

OR repair of the myelin (remyelination) may happen - sometimes spontaneously - or because of new growth of myelin-producing cells - or because nerve cells may reorganise themselves and restore electrical transmission (refM5)