Multiple sclerosis (MS) is the most common condition of the central nervous system (CNS) affecting young adults. MS is a chronic, neurodegenerative, autoimmune disorder that affects around 1 million people in the United States and 130,000 people in the United Kingdom. The global prevalence of MS (the number of people living with MS worldwide) is approximately 2.5 million.

MS causes your immune system to mistakenly attack your own body’s cells within the CNS, affecting the spinal cord, nerves, and other components of the brain. In the process, the immune system attacks and destroys the protective myelin coating on your nerve cells (neurons), a process called demyelination. People with MS can develop CNS lesions (abnormally shaped tissues), which can lead to irreversible damage to the nerve fibers and varying degrees of physical disability.

Prompt diagnosis and proper treatment are recommended to prevent future MS relapses, achieve symptom control, and improve the overall disease course. While there is currently no cure for MS, there are treatment options to control the disease progression.

What Causes MS?

At present, physicians are not sure of the exact cause of multiple sclerosis. The general consensus is that a combination of factors trigger the abnormal autoimmune response associated with the condition. Those factors include:

• Genetic factors, specifically 230 MS-linked genes
• Viral infections, such as Epstein-Barr virus
• Environmental factors, such as long-term exposure to certain toxins

Smoking tobacco products and vitamin D deficiency also increase susceptibility to MS.

Significant scientific research is underway to determine how much each factor contributes to the disease’s progression.

Who Does Multiple Sclerosis Affect?

MS can affect people of all ages, ethnicities, and sexes. That said, the condition is more prevalent among certain groups of people. In other words, certain demographic factors put some people at higher risk of developing MS.

Age

Most cases of MS are diagnosed in people between the ages of 15 and 50. However, the onset of disease can occur in people of any age — including young children. Nevertheless, the majority of those diagnosed are in their 20s and 30s.

A diagnosis of MS is also associated with a greater risk of mental health conditions, including emotional, mood, and behavioral changes.

Climate and Geography

The prevalence of MS patients increases as you travel further north or south from the equator.

Multiple sclerosis is most prevalent in the following countries:

• Europe
• The United States
• Canada
• Scotland
• New Zealand
• Parts of Australia

The parts of Asia, Africa, and America that lie on the equator have extremely low levels of MS.

The Multiple Sclerosis International Federation maintains an interactive atlas of the geographic distribution of MS. You can also download the organization’s atlas of MS, published in 2020.

Ethnicity and Race

Multiple sclerosis occurs in almost all ethnic groups. “Research has demonstrated that MS occurs in most ethnic groups, including African Americans, Asians and Hispanics/Latinos, but is most common amongst Caucasians of northern European ancestry,” according to the National Multiple Sclerosis Society.

The conditions’ prevalence is highest among white people of Northern European and Scandinavian ancestry. MS is very rarely seen in people of Inuit or Eskimo descent who live far to the north.

According to the National Multiple Sclerosis Society, “There is some evidence that MS symptoms can be different in range and severity for Black people.”

Those symptoms include:

• Higher risk of developing MS, notably in Black women
• Disease onset at a later age
• Fewer MS diagnoses
• More MS symptoms at diagnosis
• More likely to have a progressive form of MS than relapsing-remitting MS (RRMS)
• More likely to experience MS-related vision problems and mobility issues
• Less responsiveness to disease-modifying therapies

A study from the medical journal Neurology analyzed health care data from approximately 3.5 million insured Americans over a three-year period. In that time, 496 of those individuals were diagnosed with MS. Of the people diagnosed with MS, 70 percent were women and most of these women were diagnosed with RRMS.

Among the 496 individuals diagnosed with MS, African Americans were found to be at a 47 percent higher risk of developing the condition than their Caucasian American counterparts. Hispanic or Latino people were found to have half the risk and Asians had an 80 percent lower risk when compared to Caucasian people in the same cohort. The study also determined that while African American men were about as susceptible to MS as their Caucaisian male counterparts, African American women were at the greatest risk of MS.

Other Diseases of the Immune System

Immunological factors can increase your risk of developing MS. That includes having one or more additional autoimmune conditions, such as:

• Psoriasis
• Type 1 diabetes
• Lupus
• Certain thyroid problems
• Inflammatory bowel disease

Sex

Data suggests that the relapsing type of MS affects more women than it does men. Between two and three times more women have a relapsing form of MS than do men. The difference is smaller between men and women in progressive forms of MS, such as primary-progressive MS.

Physicians are not yet sure of the reason for this difference in MS incidence between men and women. Researchers believe it may be connected to sex hormones, such as testosterone and estrogen.

What Are Risk Factors for Developing MS?

Among the general population of America, the average risk of developing MS is approximately 3.5 in 1,000 — less than one half of 1 percent. MS susceptibility is affected by many factors. Risk varies across different populations or groups of people.

Genetic Risk Factors

To date, scientists have identified 230 genes linked to MS. Of these 230 genes, no single gene or genetic mutation on its own is responsible for causing the condition. Rather, which and how many of these 230 genes are impacted appears to affect a person’s likelihood of developing MS. Research is ongoing in this area.

Does MS Run in Families?

MS is not a hereditary condition. In other words, one does not inherit MS from their parents or other first-degree biological relatives. That said, one's risk of developing MS is greater if a family member has MS. That risk increases the more closely related one is to the family member with MS.

For comparison, the lifetime risk of developing MS among the general population is 1 in 330. If a first-degree relative has MS, the risk increases to between three percent and four percent. If one identical twin has a diagnosis of MS, the other twin has a 1 in 5 chance of developing MS. Nonidentical twins carry a lower likelihood of developing MS, with a 1 in 22 chance. If your biological sibling, meaning you share the same mother and father, has been diagnosed with MS, your odds of developing the condition are 1 in 37. If your parent has MS, the odds of you developing MS are 1 in 67. If you have MS and have a child, your child’s probability of developing MS is 1 in 48.

Environmental Risk Factors

Environmental factors may also affect whether a person will develop MS.

Tobacco Smoking

Smoking tobacco products, such as cigarettes and cigars, is generally unhealthy — but especially if you are at risk of developing MS. Women who smoke are 1.6 times more likely to develop MS than women who are nonsmokers. Individuals with MS who smoke also appear to be at a much greater risk of experiencing a more rapid progression of their disease.

Sun Exposure and Vitamin D

Vitamin D deficiency and exposure to sunlight may lower one’s risk of developing MS. Data suggests that women who take at least 400 international units or vitamin D daily are at lower risk of developing MS. Populations exposed to more sunshine or ultraviolet rays appear to have lower rates of MS.

Talk With Others Who Understand

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 165,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Are you living with multiple sclerosis? Share your experience in the comments below, or start a conversation by posting on your Activities page.