Most scientists agree that no single virus or bacterium causes multiple sclerosis (MS) all by itself. They have also concluded that no single thing in the environment or in a person’s diet is directly responsible for the disease.
Currently, scientists believe that the disease is caused by a combination of several factors — including gender, racial/ethnic, geographic, genetic, and lifestyle factors that interact with an infectious trigger of some kind (for example, one or more viruses or bacteria) to stimulate the autoimmune process. When a person with a genetic susceptibility to MS meets up with environmental triggers, his or her immune system overreacts in a way that sets off the abnormal autoimmune process.
Why some people get MS and others don’t remains a mystery. Solving this mystery is important because identifying the factors that make some people susceptible to MS and others not would help scientists figure out the cause of MS. And identifying the cause would make it a whole lot easier to find more effective treatment and, eventually, a cure.
Multiple sclerosis: Gender factors
The fact that MS doesn’t occur equally in women and men has long piqued the curiosity of scientists and physicians. It turns out that some interesting differences exist between the sexes (in regard to MS, that is) that may provide important clues to the cause of MS:
MS is two to three times more common in women than in men. However, prior to the onset of puberty, boys are as likely to get MS as girls.
Men tend to develop MS at a later age than women do, and they’re more likely than women to be diagnosed with primary-progressive MS.
Multiple sclerosis: Ethnic or racial factors
MS isn’t unique to one racial or ethnic group, but certain groups are much more susceptible than others. Scientists are using the following clues to help themselves understand the genetic and environmental factors that may be causing these group differences:
MS is most common among Caucasians of northern European ancestry.
African-Americans and Hispanics develop MS half as often as Caucasians.
Asians develop MS less frequently than Caucasians and generally have different types of symptoms.
MS is rare (or unheard of) in pure Africans, Inuits, and some isolated populations around the world that have never mingled with other groups.
Multiple sclerosis: Geographical factors
The geographical distribution of MS has been known for a long time: In general, the further you live from the equator, the greater your chances are of developing MS. Like a lot of other aspects of MS, no one knows why this is true, but here are some possible explanations:
Genetic/ethnic: Residents in the temperate areas of the world (except certain groups like the Inuits) tend to be of northern European descent.
Climatatic/meteorologic: Residents of the tropics have greater exposure to the sun and vitamin D, which may offer some protection against MS.
Infectious: Certain types of infectious agents may be more common in temperate areas of the world.
Each of these possible explanations is the subject of intensive investigation.
Multiple sclerosis: Genetic factors
MS isn’t an inherited disease. However, the evidence is quite strong that a genetic factor contributes to a person’s risk of developing MS. The following facts point to a genetic component:
Approximately 20 percent of people with MS have a close or distant relative with MS.
The risk for someone who has one close relative with MS is 3 to 5 percent (compared to less than 1 percent in people without a relative with MS). For a person in a multiplex family — which has several members with MS — the risk of developing MS is even higher. Keep in mind, however, that even within the same family, close relatives can experience different disease courses, symptoms, and levels of disability.
If one identical twin develops MS, the risk for the other twin is about 30 percent — proving that the disease isn’t directly inherited. Because identical twins share identical genetic traits, the risk would be 100 percent if genetics told the whole story.
Multiple sclerosis: Lifestyle factors
You’ve probably asked yourself (and your doctor) a hundred times what you did — or didn’t do — to cause your MS. Just remember that it’s clear from the study of geography, ethnicity, and genetics that the cause of MS — whatever it turns out to be — isn’t anything simple or direct. You didn’t do anything to cause MS to happen.
However, here are some intriguing findings related to lifestyle:
Even though exposure to sunlight and vitamin D is primarily determined by how close to the equator a person lives, it may also be related to time spent outdoors. One study found that people who got extra vitamin D from a daily multivitamin were at a lower risk for MS.
Some studies have suggested that dietary factors may play a role in determining a person’s susceptibility to MS. For example, it has been suggested that Inuits don’t get MS because of their fish-heavy diet.
Several studies have suggested that smoking increases a person’s risk of developing MS as well as the risk for disease progression, but no one has a clue why this may be true. So, if you’re looking for yet another reason to quit smoking, its possible relationship to MS is a good one.