Multiple sclerosis (MS) causes a wide range of symptoms involving the brain, optic nerves, and spinal cord. Research is only just beginning to reveal who is at risk and what causes the condition.

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MS is a chronic condition affecting 2.8 million people worldwide. While treatment options are currently limited, trials of several new approaches are underway.

Researchers believe that MS is an autoimmune disorder. This type of illness involves the immune system attacking healthy cells, much as it would attack viruses or bacteria.

In the case of MS, the immune system attacks the myelin sheath that surrounds nerve cells. The attack causes lesions to form, and over time, these cause scarring, which leads to nerve damage and reduced function.

As a result of this damage, a person with MS may experience numbness and tingling sensations, fatigue, muscle weakness, dizziness and vertigo, memory issues, and vision problems, among other symptoms.

There are four types of MS: clinically isolated syndrome (CIS), relapsing-remitting MS, primary progressive MS, and secondary progressive MS.

CIS is a single episode of MS-like symptoms that lasts for at least 24 hours. People with CIS do not necessarily have MS, but experiencing an episode can be the first sign of the condition.

Treating MS involves interdisciplinary care, including rehabilitation, disease-modifying drugs (DMARDs), and complementary and alternative therapies.

Scientists do not fully understand the risk factors for MS and the mechanisms of the condition. However, they are making new headway in the search for answers and improvements in treatment.

What does the latest research show about the risk factors, mechanisms, and treatments of MS? In this Special Feature, Medical News Today takes a closer look.

French neurologist Jean-Martin Charcot first described the features of MS in 1868. He noted the differences between this condition and the tremor of paralysis agitans, a symptom of the neurological condition later named Parkinson’s disease.

The three symptoms associated with MS at the time were called Charcot’s triad. They included a characteristic tremor, involuntary eye movements, also known as nystagmus, and scanning speech, which some call staccato or explosive speech.

Decades later, the invention of MRI scans helped doctors diagnose MS. Treatment with steroids became commonplace, and doctors then began to use medications in a class of drugs called interferons. The Food and Drug Administration (FDA) first approved interferons for use in people with MS in 1993.

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Although scientists and healthcare professionals understand the defining features of MS, several aspects of the condition remain a mystery.

While researchers recognize that MS is an autoimmune condition, they do not understand why immune cells attack myelin.

Also, diagnosing MS is still an ambiguous process because its symptoms are similar to those of many other health conditions.

In addition, experts do not know why women are 2–3 times more likely to be diagnosed with MS than men.

Research suggests that risk factors of MS include a lack of vitamin D or sunlight, smoking, obesity, a history of infection with the Epstein-Barr virus, being female, and possibly having inherited specific genes, as well as environmental factors.

More recently, the gut microbiota has emerged as a possible risk modulator.

A recent overview of clinical research found that people with MS had larger populations of Pedobacteria, Flavobacterium, Pseudomonas, Mycoplana, Acinetobacter, Eggerthella, Dorea, Blautia, Streptococcus, and Akkermansia bacteria in their intestines than people without MS.

People with MS also had reduced populations of Prevotella, Bacteroides, Parabacteroides, Haemophilus, Sutterella, Adlercreutzia, Coprobacillus, Lactobacillus, Clostridium, Anaerostipes, and Faecalibacterium bacteria.

Researchers speculate that balancing out the populations of gut bacteria in people with MS may reduce inflammation and the overactivation of the immune system.

Research from the MS Society Edinburgh Centre for MS Research found that people with MS had reduced numbers of inhibitory neurons, compared with people who did not have the condition.

However, people with MS had as many stimulating neurons as those without the condition. This was true even for people who had received their MS diagnoses many years earlier.

These findings help reveal the types of neurons affected by MS, shedding more light on how the condition evolves within the body. The research may also offer insight into treatments that could protect the targeted neurons.

DMARDs that health authorities have recently approved as MS treatments include cladribine (Mavenclad) and siponimod (Mayzent) for relapsing-remitting and active secondary progressive forms of the condition.

Cladribine targets lymphocytes, white blood cells responsible for attacks on myelin. Siponimod harnesses specific white blood cells that attack myelin and prevents them from circulating in the body.

However, due to their interactions with the immune system, these drugs may lead to a reduction in lymphocytes, making a person vulnerable to infections.

The medicines’ actions may also contribute to reduced responses to vaccines in people who receive routine vaccinations. With the introduction of COVID-19 vaccines, scientists have investigated whether people with MS who take medications such as cladribine can have adequate responses to vaccines.

The latest research indicates that people taking cladribine do produce protective antibodies to other common vaccines, despite having decreased lymphocyte levels induced by the medication.

This result gives scientists and others in the medical community hope that people who take these drugs for MS will have similarly adequate responses to COVID-19 vaccines.

Some scientists are currently investigating the potential for stem cell therapy for MS. In a phase 1 study conducted at the Karolinska Institute, in Stockholm, Sweden, seven people with progressive MS received infusions of stem cells derived from each participant’s own bone marrow.

As early as 7 days after administration of the stem cell therapy, researchers found evidence of positive changes in the participants’ immune systems. At 12 weeks, five out of six participants had no new characteristic lesions on follow-up MRI brain scans.

As their understanding of the condition evolves, many scientists are investigating the root cause of MS.

An analysis of the current data has revealed a possible connection between gut health and the condition. Data revealing relationships between the gut microbiota and the brain continually emerge, and scientists are hopeful that diet modifications, probiotics, and certain drugs that balance the gut microbiome will play a role in MS treatment.

Also in development are remyelination and neuroprotection therapies. The latter aim to protect the axons and myelin from further damage, while the former could restore lost function for people with MS.

Meanwhile, immunotherapy drugs would protect the nerves from destruction and rebuild neurons that have already sustained damage.

Another potential treatment in phase 1 trials is a tumor necrosis factor-alpha (TNF-alpha) inhibitor called MYMD-1. TNF-alpha is a type of cytokine produced by white blood cells that regulates some aspects of the immune system.

Overproduction of this cytokine is associated with several autoimmune conditions, including MS. MYMD-1 is a new type of TNF-alpha blocker that shows promise as a treatment for MS and other conditions.

Trials for therapies involving the gut microbiome, stem cells, neuroprotective treatments, remyelination, and MYMD-1 are still in the earliest stages. However, the possibilities provide hope that ongoing research will lead to effective ways to prevent MS and better methods of treatment.