Multiple sclerosis (MS) is a disease that affects the central nervous system, including the brain and spinal cord. Over time, it can cause permanent nerve damage.

People with MS may develop a variety of symptoms, such as muscle stiffness and spasms, difficulties with movement, and vision loss.

While the exact cause of MS is not known, research into this condition continues. Read on to learn more about the causes of MS, and how to treat it.

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Research indicates that environmental factors may increase the risk of MS.

MS is a demyelinating disease, which means it affects nerve tissue. Most experts believe it is an autoimmune condition.

“This means that the body’s defenses, called the immune system, mistakenly attack normal tissues,” Dr. Benjamin Segal, M.D., chair of the neurology department and co-director of the Neurological Institute at The Ohio State University Wexner Medical Center in Columbus, tells Medical News Today (MNT).

In people with MS, an abnormal immune response causes inflammation and damage to areas of the myelin sheath. This sheath is a protective coating of fat that surrounds nerve fibers, and the myelin sheath is necessary for the effective transmission of nerve messages throughout the body.

When the immune system damages the myelin sheath, it impairs transmission between the underlying nerves. This disrupts communication between the central nervous system, which includes the brain, spinal cord, and optic nerves, and other body parts.

This causes symptoms of MS, such as muscle spasms and vision loss. Demyelination and symptoms come and go in episodes with relapsing-remitting MS. However, in progressive forms of the condition, they gradually get worse and do not improve.

Experts do not know what exactly triggers the autoimmune response in MS. They believe a combination of genetic and environmental factors play a part.

“We don’t have a clear understanding of the etiology of multiple sclerosis,” Dr. Asaff Harel, M.D., a neurologist and MS specialist at Lenox Hill Hospital in New York, NY, tells MNT.

“There’s clearly some genetic predisposition, but there are also environmental factors, and we don’t really understand how those interact,” he says.

Genetic risk factors

No single gene directly causes MS. However, many genetic variants increase a person’s chances of developing the disease.

“More than 230 genes have been discovered that each increase the risk of developing MS to a small degree,” Dr. Segal explained. “Someone with MS is likely to have a combination of many of these MS-associated genes,” he adds.

Most MS-associated genes play a role in the immune system. For example, the U.S. National Library of Medicine report that one particular mutation in the HLA-DRB1 gene is the strongest genetic risk factor for MS. HLAgenes help the immune system distinguish between the body’s proteins and foreign organisms, such as viruses.

If a person has an MS-associated genetic mutation, they may pass it on to their children. As a result, people with a family history of MS are more likely to develop it themselves.

Scientists continue to investigate the role that different genes play in MS.

Lifestyle and environmental risk factors

Researchers suggest the environmental factors that may increase the risk of MS include:

  • Exposure to certain viruses: According to a review in The Lancet Neurology, evidence suggests that people who contract the Epstein-Barr virus have an increased risk of MS. This virus causes infectious mononucleosis, or “mono.”
  • A history of smoking: The authors of the same review article indicate that studies consistently link people who smoke with a heightened risk of MS.
  • Low blood levels of vitamin D: In Neurology and Therapy, scientists report that a growing body of evidence links low vitamin D levels to a higher risk of MS.
  • Living farther from the equator: An analysis in The Lancet Neurology indicates that MS is more common in regions that are farther from the equator.

It is difficult for scientists to accurately determine if these factors contribute to the development of MS, or if they are markers for other conditions that do.

“It’s unclear which are just markers and correlations, and which are causative,” Dr. Harel says. “Causation is really difficult to prove,” he adds.

Scientists continue to study these potential risk factors, and others.

Medical experts can help treat MS with disease-modifying therapies (DMTs).

These medications target specific cells or molecules in the immune system. For example, certain DMTs help kill, limit the growth, or block the movement of immune cells that cause inflammation and damage to the myelin sheath in MS.

A person who takes DMT may help limit inflammation and impairment of their central nervous system. This may help delay or prevent the development of the disability.

Only one type of DMT has U.S. Food and Drug Administration (FDA) approval to treat primary progressive MS. However, the agency has approved multiple DMTs to treat relapsing-remitting MS, and active secondary progressive MS.

As scientists learn more about the roles that different immune cells play in MS, they may develop additional treatments.

A doctor can examine a person’s medical history and treatment needs, to determine which DMT may be suitable for them.

“Neurologists may prescribe a specific disease-modifying drug depending on the type of MS a patient has, their symptoms, sensitivity to potential side effects, and how they have responded to alternative disease-modifying treatments in the past,” Dr. Segal says.

“These drugs differ in effectiveness, potency, side effects, and risk factors for adverse effects,” he adds.

A person’s healthcare provider may also prescribe other treatments to help manage symptoms or complications of MS, including:

  • other types of medication to help control symptoms
  • physical therapy, occupational therapy, or speech therapy
  • the use of a mobility device or other assistive devices
  • mental health counseling
  • lifestyle changes

“Each [treatment] comes with a different sort of benefits and risks,” Dr. Harel says, “and it’s important to discuss the pros and cons of each to help a patient make an informed decision.”

Here are some frequently asked questions about MS risk factors and causes.

What is the strongest risk factor for multiple sclerosis?

Some research suggests that changes in the HLA-DRB1 gene are the strongest genetic risk factors for MS. Exposure to certain viruses, such as the Epstein-Barr virus, can also increase a person’s risk of MS.

What is the leading cause of multiple sclerosis?

The exact cause of MS is unclear. It happens when the immune system mistakenly attacks healthy tissue in the brain. This causes inflammation and damage to the myelin sheath, which can lead to symptoms such as muscle spasms and changes in vision.

Experts generally believe that MS is a demyelinating autoimmune disease, but they do not fully understand why it develops.

Scientists know many different genetic variants that appear to raise the risk of MS. Studies suggest that exposure to certain viruses, a history of smoking, and other environmental factors may also contribute to the development of the disease.

To treat MS, a doctor will likely prescribe a DMT that targets cells and molecules in a person’s immune system. They may also recommend other treatments to help manage the symptoms and complications of MS.

People should talk to their doctor to learn about the potential benefits and risks of these different treatments.