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.

MS isn’t 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

Does MS run in families? Among the general population in the United States, the odds of developing MS are about 1 in 333, according to the National Multiple Sclerosis Society. An identical twin whose sibling has MS, however, has a 1 in 4 chance of developing MS.

More than 200 genes have been linked to MS.

Many family members and caregivers of people with MS may wonder things like: Can MS be passed from parent to child? If my brother has MS, should I be tested? Is MS hereditary from my grandmother? Although there’s no single gene linked to MS, a 2013 analysis of 18 studies found the lifetime risk of developing MS for family members is:

• 1 in 5 if an identical twin has MS
• 1 in 22 if a nonidentical twin has MS
• 1 in 37 if a sibling has MS
• 1 in 67 if a parent has MS

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

Although the cause of MS is unknown, scientists have found that genetic factors play a role in susceptibility and the development of MS. More than 200 genes have been linked to MS, and people with the disease may have one risk factor or a combination of genetic factors. The 2013 study calculated that genes contribute to 54 percent of MS risk factors.

3. Environmental Factors

With MS, an abnormal immune system response causes inflammation and damage to the central nervous system and the myelin sheath protecting 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)

One environmental factor that has been thought to cause 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 developing 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 developing MS.

4. Vitamin D Status

Low vitamin D levels in the blood have also been linked to an increased risk of MS. Researchers are investigating the role of vitamin D supplementation in supporting immune system function, which could protect against immune-related diseases such as MS.

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

Talk With Others Who Understand

On MyMSTeam, the social network and online support group for people with MS and their caregivers, more than 217,000 members talk about a range of personal experiences, including asking questions about MS and heredity.

Do you have multiple cases of MS in your family? Do you think environmental risk factors, genetic variants, or other factors placed you at higher risk of multiple sclerosis? Share your thoughts and experiences in a comment below, or start a conversation on your Activities page.