If you have 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. MS is not hereditary, meaning it’s not directly transmitted from parent to child or passed down in a family through generations. However, having a first-degree relative with MS does raise a person’s risk of developing the condition.

Here are some of the key factors that affect the risk of MS.

1. Immediate Family History of MS

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.

A 2013 analysis of 18 studies found the following lifetime risks of developing MS for family members:

• 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

Read about how MS affects life expectancy.

Multiple sclerosis may affect just one generation. “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 or a combination of genetic factors. The 2013 study calculated that genes contribute to 54 percent of MS risk factors.​

3. Environmental Influences

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 factors in the internal and external environment.

Environmental factors for MS include:

• Viruses (such as the Epstein-Barr virus)
• Infections
• Smoking
• Geographical location (including the northern U.S., southern Canada, parts of Europe, southern Australia, and New Zealand)

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 “Is MS Curable Yet? Dr. Boster on Research Advances.”

5. Extended Relatives With MS

Having a 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 clan — 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.

Some MyMSTeam members expressed concern that their doctors didn’t look for MS. “My mom and I have MS,” reported one member. “Neither of our neurologists asked for medical histories, where we’ve lived, or run medical tests to understand why two people in the same family developed the same ‘noncontagious, nonhereditary’ disease. I’m completely perplexed.”

Learn more about early symptoms of MS.

You Are Not Alone: Finding Support for MS

On MyMSTeam, the social network and online support group for those living with MS, more than 206,000 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 a vitamin D deficiency, genetic variants, or other factors placed you at higher risk of MS? Share your thoughts and experiences in a comment below, or start a conversation on your Activities page.