If you’ve been diagnosed with multiple sclerosis (MS) — an autoimmune disease that attacks nerves in the spinal cord and brain — you may worry about passing it on to your children. If you’re a caregiver for someone with MS, you may be concerned that you or others in your family are at risk for MS.

Does MS run in families? MS isn’t strictly hereditary, which means it isn’t directly passed from parent to child or passed down in a family through generations. However, having a first-degree relative with MS can increase a person’s chances of developing the condition.

Here are some of the key genetic and environmental factors that can affect a person’s risk of MS.

1. Immediate Family History of MS

Many family members and caregivers of people with MS may have questions like: Can MS be passed from parent to child? If my brother has MS, should I be tested? Is MS hereditary from my grandmother?

Among the general population in the U.S., the odds of developing MS are about 1 in 333, or less than half of 1 percent, according to the Multiple Sclerosis Society of America. However, studies show that the risk of developing MS is higher for people with immediate family members who also have MS. People with a parent, child, or sibling with MS have a 3 percent to 4 percent risk of developing MS.

A 2013 analysis of 18 studies helped researchers understand the lifetime risk of developing MS for family members. Researchers found that, overall, the risk of MS is highest for family members who are more closely related to someone with MS. For example, the risk of developing MS for an identical twin whose sibling has MS is between 20 percent and 25 percent. The lifetime risk of developing MS for other family members of a person with MS is as follows:

• Nonidentical twin — 4.5 percent
• Sibling — 2.7 percent
• Parent — 1.5 percent
• Child — 2 percent

These numbers suggest there may be a genetic component to MS. However, you can get MS even if nobody in your family has it. Also, multiple sclerosis may affect your generation without having affected your parents’ generation or vice versa. “All my siblings have it,” said one MyMSTeam member. “My oldest sister has been diagnosed. My younger sister and brother have symptoms but won’t get diagnosed. No one in our family that we know of has it except us. Weird.”

Some MyMSTeam members urged others to share complete family histories with doctors. One described this experience: “My brother was having problems with his vision, and the doctor couldn’t pinpoint the problem. I asked him, ‘Did you tell the doctor your sister has MS?’ The answer was no. As soon as he did, they tested him for MS, and guess what?”

2. Genetic Risk Factors

There’s no single gene linked to MS. Although the cause is unknown, scientists have found that genetic factors play a role in susceptibility and the development of MS. About 230 genome-wide significant risk variants have been linked to MS. People with MS may have one genetic risk factor, or a combination of risk factors.

The 2013 study calculated that genes contribute to 54 percent of MS risk factors. Although having genetic risk factors can raise your likelihood of developing MS, they don’t determine your destiny.

3. Environmental Factors

With MS, an abnormal immune system response causes inflammation and damage to the central nervous system and the myelin that protects the nerves. This process is likely influenced by a combination of factors in the internal and external environment.

Some environmental factors that are linked to MS include:

• Infections
• Smoking
• Geographical location (including the northern U.S., southern Canada, parts of Europe, southern Australia, and New Zealand)
• Obesity in adolescence or early adulthood

One environmental factor that has strong evidence to support a causal role in developing MS is Epstein-Barr Virus (EBV), which causes mononucleosis (“mono”). One 2022 study published in Science found that people who had EBV had 32 times the risk of MS. However, it’s important to note that most people who have EBV never develop MS.

A 2022 study showed that people who had Epstein-Barr Virus had 32 times the risk of MS.

4. Vitamin D Status

Vitamin D is an important nutrient that supports your bones, muscles, immune system, and brain. You get vitamin D from the sun and some foods, like fish, eggs, and milk. A growing number of studies support that vitamin D may have a protective role for MS.

Having low levels of vitamin D in the blood has been linked to an increased risk of developing MS. Researchers have found that people with naturally low vitamin D levels are more likely than the general population to develop MS. This may be especially true for people who have low vitamin D levels at birth or in childhood. Although having low vitamin D levels is associated with a higher risk of MS, there is no evidence that high vitamin D levels can protect against MS.

Researchers are also investigating the role of vitamin D supplementation in supporting immune system function, which could be beneficial for people with MS. However, the results of randomized clinical trials have been mixed. In a 2025 randomized clinical trial published in JAMA, researchers found that high doses of vitamin D reduced disease activity in people with clinically isolated syndrome and early MS. In previous clinical trials, researchers found no difference in disease activity in those taking vitamin D.

Research on MS is advancing our understanding of this chronic disease. Read “Will There Ever Be a Cure for MS? Dr. Boster Explains Research Advances.”

5. Extended Relatives With MS

Having a more distant relative with MS poses less risk than having a parent or sibling with the condition. Still, some members of MyMSTeam have described MS occurring outside their immediate family.

• “Six people in my family (including myself) have relapsing MS.”
• “I was diagnosed first, then my sister, who died from complications. Now my niece has it.”
• “My first cousin and my aunt’s granddaughter have it, all on my dad’s side.”
• “A cousin and an aunt, both on my maternal side.”

MyMSTeam members with no family history of MS were surprised when they — or someone in their circle — received a diagnosis. “We were shocked when my daughter was diagnosed just before her 20th birthday. How could this be? Where did it come from? Then, three years later, I was diagnosed at age 57,” one member said.

Remember that genetics is just one of several factors that play a role in MS development. No single factor has been proven to cause MS. Learn more about early MS symptoms.

Join the Conversation

On MyMSTeam, people share their experiences with MS, get advice, and find support from others who understand.

Do you have multiple cases of MS in your family? Let others know in the comments below.