How do people develop multiple sclerosis?



Multiple sclerosis (MS) occurs as a result of damage to the nerve fibers of your central nervous system.

Your central nervous system consists of your brain and spinal cord, and it is responsible for controlling every action of your body, conscious and unconscious.

When you perform an action, your brain sends messages to the appropriate part of your body via the nerve fibers in your spinal cord. These nerve fibers are covered by a substance called myelin, which helps carry the messages from your brain quickly and smoothly.

In MS, the myelin on your nerve fibers becomes damaged, which disturbs the messages sent from your brain. MS is an autoimmune condition, which means that your body's own immune system mistakes the myelin for a foreign body and attacks it. This process is called demyelination.

The myelin becomes damaged, and develops scars called lesions, or plaques.

Demyelination disrupts the messages travelling along nerve fibers, slowing them down, jumbling them, accidentally sending them down a different nerve fiber, or stopping them from getting through at all.

Over time, the myelin can be completely broken down and the nerve fibers themselves can become damaged. It is this nerve fiber damage that causes the progressive forms of MS, in which symptoms steadily worsen.

Why do people develop multiple sclerosis?

It is understood that MS occurs as autoimmune response; where your own immune system mistakes myelin on the nerve fibers of your central nervous system for a foreign body, and attacks it.

However, what it is not understood is what causes this autoimmune response in the first place, although there are several theories.

Most experts agree that MS is most likely caused by a combination of genetic and environmental factors. This means that it is partly due to the genes that you inherit from your parents, and partly due to outside factors which may trigger the condition.

The possible causes of MS are detailed below.

Genetic factors

Genes carry the information from your parents that determines your physical characteristics, such as hair and eye color. Genetic conditions are caused by a defect or abnormality in a gene, which is passed on to a person and is present in them from birth.

MS is not defined as a genetic condition because there is no single gene that causes it. It is not directly inherited from one member of a family to another, although research shows that people who are related to someone who has MS are slightly more likely to develop it, than those who are not. However, the chances of MS occurring more than once in a family are very small, and there is only a 2% chance of a child developing MS when a parent has it.

It is possible that there a combination of genes that make developing MS more likely, and research is continuing into this.

However, the fact that only a relatively small number of people in the general population go on to develop MS suggests that its causes cannot be simply down to genetics.

Environmental factors

Research into MS around the world has shown that it is more likely to occur in countries that are far from the equator. For example, MS is relatively common in North America and Scandinavia, but hardly ever occurs in countries such as Malaysia and Ecuador.

The reason for this is not fully understood, but it is thought that MS could be triggered by a particular bacteria or virus which thrives in a cooler environment. Some experts believe that a common childhood infection in these cooler countries may disturb the immune system or trigger an autoimmune response in some people, which goes on to develop into MS.

As yet, no bacteria or virus has been identified to back this up. However, research has shown that people over the age of 15 who move away from countries nearer to the equator to a cooler climate, still have a lower risk of developing MS than those who are born there.