Last updated: Oct 15, 2014

Multiple sclerosis is pretty quirky as far as diseases go—and some of the nuances surrounding it continue to baffle experts. What they do know for sure: MS is an autoimmune disease that occurs when the body misfires against its own central nervous system. A few things linked to a higher risk:

1. Your gender

Montel Williams and a few other high-profile male celebrities have been diagnosed with MS, but by and large, MS disproportionately strikes women, says Nancy L. Sicotte, MD. And the gender gap is growing: "It used to be two women to every one man, but several new studies suggest that the ratio is approaching 4-to-1," she says. Even though the disease is more common among women (they are also more likely to get MS at a younger age), it tends to be more severe in men, adds John Rose, MD, professor of neurology at the University of Utah.

2. Where you live

People who dwell nearer the earth's poles (think Australia, New Zealand, Canada and Iceland) are more likely to get MS than those who live closer to the equator. This is true in the United States, too: MS is about twice as prevalent in North Dakota as in Florida, for example. Researchers believe that vitamin D, or lack thereof, is the reason. Our bodies produce D in response to sunlight, so people far from the equator make less, especially during the long, dark winter months.

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3. Having moved as a child

If your family relocated when you were growing up, your risk of MS may change to reflect your new homeland, whether you go from a low-risk area for MS or vice versa. However, this is true only if you moved before the age of 15.

4. Your DOB

Strange but true: Finnish researchers found that spring babies have a higher risk of MS. (In the study, an April birth was linked to a 9.4 percent higher MS risk, while those born in November had an 11.1 percent lower risk.) A possible explanation, according to Dr. Rose: "If your mother was pregnant with you through the winter, her levels of vitamin D during pregnancy may have been low."

5. Your ethnicity

MS is more common among Caucasians, particularly those with northern European ancestry. Some groups, such as people with African, Asian, Hispanic and Native American ancestry—, seem to be at lower risk, although they can still get the disease. MS is almost unheard of among some groups, including Australian aborigines and New Zealand Maoris, according to the National Multiple Sclerosis Society.

6. Your smoking status

We all know that puffing is bad news and that it increases the odds of lung cancer and heart attack or stroke. But did you know it's a well-established risk factor for MS, too? Smokers and ex-smokers are more likely to get MS than people who never smoked, and the more cigarettes you've had, the greater your chances (people who smoke at least two packs a day have a fivefold greater risk). While you can't erase the past, quit if you haven't already: MS may progress more quickly in current smokers, according to research.

7. Your age

You can be diagnosed with MS at almost any time, from childhood right on up to your years as a senior citizen, but it's most liable to strike from age 20 to 50. "MS is not an all-comers' disease," says Carrie Lyn Sammarco, DrNP. "We don't tend to see it in children, although it can occur."

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8. You've had mono

Many germs have been studied as possible MS triggers, but the results have been mixed. There is, however, a growing body of evidence that Epstein-Barr virus (EBV), which causes mononucleosis, is a culprit. A Journal of the American Medical Association study found higher levels of EBV antibodies in people with MS. (About 90 percent of people are infected with EBV at some point, although not all get symptoms.) And researchers at Wayne State University in Detroit found that a history of EBV is more common among people with MS. While it's not certain whether the virus causes MS, "a relationship is clearly present," they concluded.

9. You have another autoimmune condition

Autoimmune diseases tend to cluster, so if you have one, you may develop others. That means if you have inflammatory bowel disease or type 1 diabetes, you may have a slightly higher risk of being diagnosed with MS, too. (The link isn't as strong with some autoimmune diseases, such as lupus and rheumatoid arthritis.) "Genes seem to haywire the autoimmune system," Dr. Rose explains.

10. Your family tree

While environmental factors have an impact on your chances of developing this disease, so do genetics. "If a mom or dad has MS, their children have between a 5 and 10 percent chance of getting it," Dr. Rose says. The MS risk is 1 in 750 for most people, 1 in 40 for those with close family members with the disease and 1 in 4 for those with an identical twin who has it.