Both genetic and environmental factors play a role in the development of multiple sclerosis (MS), which is an autoimmune disease.

Some diseases are purely genetic, which means a person will get the disease if they inherit one or two copies of a specific gene. MS is not genetic in this way.

However, research shows that certain genetic variants increase the risk of developing MS. MS also tends to run in families, suggesting a genetic role.

Keep reading for more information about how genetics could cause MS, other causes, diagnosis, and treatment methods.

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Multiple sclerosis is an autoimmune disease, which means it occurs when the immune system attacks healthy tissue. Over time, the immune system gradually attacks the myelin that protects nerves, contributing to the death of neurons in the brain and spinal cord.

This can affect many areas of functioning. For most people, the disease begins with pain, weakness, or mobility issues. A person might have tingling in their hands or legs, tremors, unexplained pain, or sudden difficulties with balance.

Over time, as the immune system attacks and damages more of the central nervous system, symptoms will get worse without treatment. Some symptoms include:

  • mood changes, such as depression or anxiety
  • trouble concentrating or remembering things
  • increasing mobility impairments that may necessitate the use of wheelchairs or other assistive devices
  • incontinence
  • vertigo
  • ringing in the ears
  • sensory issues, such as changes in vision or hearing

Researchers have not found a single gene or combination of genes that cause MS or make the development of MS inevitable. However, they have identified a number of genes that seem to increase the risk of MS.

With certain disorders, a person will inevitably get the disease if they carry a gene for it. MS is not such a disorder. There are at least 200 genes that may increase the risk of developing MS, especially in the presence of certain environmental conditions.

Studies of twins suggest that if one twin has the disorder, the other is also more likely to get it. However, twins usually share environmental factors, too, especially when they are young, so both genetic and environmental factors may explain this phenomenon.

A 2014 population-wide study in Sweden estimates heritability for MS at 35–75%. It is important to note that this study does not reference the ethnicity of the population sample.

Heritability is a measure of the percentage of difference between groups that is due to genetics. So, for example, if a trait has 100% heritability, genetics explain all differences, while 0% heritability means that genetics do not play a role at all. The heritability figure for MS suggests that genetic factors are important, but are not the only factor contributing to the development of MS.

Some diseases show a specific pattern of inheritance, such that if a person carries a gene, they will inevitably develop a disorder. In other cases, a person might carry a gene for a disorder with no symptoms but pass that gene on to a child. If their partner also carries the gene, the child will have the disorder.

MS does not follow this predictable pattern of inheritance. Researchers have identified hundreds of genes that seem to increase the likelihood of MS. However, no single gene appears to make MS inevitable. Neither does it make MS inevitable when combined with another such gene.

A person’s chances of getting MS are higher if a close relative, such as a parent or sibling, has the disease. Identical twins will both have MS in 20–30% of cases, while non-identical twins will both have the disease in about 5% of cases.

Some research has found that people living in certain geographic regions are more vulnerable to MS. This might mean that genetic factors are more prevalent among these populations.

However, a 2007 study found that people who migrate to areas where MS is more common develop a similar risk for the disease as those previously living there.

Researchers require more data to determine whether there is a predictable pattern of inheritance for MS and how certain genetic risk factors interact with the environment.

It is likely that the interaction between genes and environment causes a person to develop MS. For example, some research shows that epigenetic factors contribute to MS. Epigenetics is the study of gene expression (whether a gene “turns on” and why).

Exposure to toxins such as smoking and pollution may change the behavior of genes. So can deficiencies of certain vitamins, such as vitamin D. Injuries and illnesses may also increase inflammation, further changing the behavior of genes and increasing the likelihood that a person with a high genetic risk for MS develops symptoms.

Some risk factors that may make MS more likely include:

  • Infections: Certain infections, such as the Epstein-Barr virus that causes mononucleosis, may increase the risk of developing MS.
  • Smoking: People who smoke are more likely to develop MS.
  • Obesity: Obesity may increase the risk of MS, especially if a person has obesity in childhood. Researchers do not know whether obesity leads to MS or if it occurs more frequently in people at high risk for MS.
  • Nutritional deficiencies: Certain vitamin deficiencies, especially vitamin D, may raise the risk of MS.
  • Toxins: Some researchers believe exposure to certain toxins might increase the risk of MS, but this theory is controversial.
  • Diet: Some studies have found a correlation between MS and certain changes in the gut microbiome.

A doctor diagnoses MS based on symptoms and ruling out other potential causes. They then look for MS-related damage to the nervous system. This may require a combination of blood tests, medical questions, and imaging scans of the brain and spinal cord.

Some treatment options include:

  • Disease-modifying drugs: The aim of these drugs is to slow down the immune system’s attack on the central nervous system, but they also weaken the immune system. Some people have side effects or develop a weaker immune system.
  • Pain medication: Some people take pain medication to manage MS symptoms.
  • Support: Living with MS can be difficult. Information, support from family, and psychotherapy may help.
  • Psychoactive drugs: Drugs to deal with depression and anxiety may ease these symptoms of MS.
  • Physical and occupational therapy: Occupational or physical therapy may help a person regain some strength and function and help them with their daily routine.

MS is a chronic and often progressive disease. There is no cure, but treatment can reduce symptoms. In many cases, treatment may even send the disease into remission, allowing a person to live symptom-free for long periods.

Learn more about living with MS here.

MS is a serious illness, and many people experiencing it may struggle to understand the cause.

Doctors do not fully understand what causes this disease. However, there seems to be a combination of genetic and environmental factors that are responsible.

Doctors also remain confused as to why some people with many risk factors may not develop MS, while those with few risk factors do.

More research may shed light on how MS begins and on how best to treat it.