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What is MS?


The Demographics of MS

In Canada there are approximately 50,000 people living with MS. Nearly three cases are diagnosed every day. The Multiple Sclerosis Society of Canada estimates that there are approximately three million people living with MS worldwide. In Canada, prevalence rates range from one MS case per 500 people to one in 1,000.

Risk Factors

Who is most likely to contract multiple sclerosis and why? Scientists don't have all the answers but continue to search for clues that will someday unlock these secrets. In the past several decades much information has become available suggesting that MS is a complex, singular disease that is determined by both environmental and genetic influences. Actually, more is understood about the demographic and clinical features contributing to MS than is known about the course of the disease.

Let’s examine the following common factors that may be associated with MS:

  • Genetics
  • Sex
  • Age
  • Geographic location
  • Race
  • Socioeconomics
  • Viruses


Many theories in medical literature point to the likelihood that certain people may be born with a hereditary link toward acquiring MS. We know that having a close relative such as a parent, brother or sister with MS slightly increases one's chances of developing the disease. Though this genetic tendency has not been proven, some research suggests that certain people may possess genetic characteristics that make them more likely to respond to environmental factors that trigger the onset of MS symptoms.

Studies of identical and fraternal twins, and non-twin siblings revealed that when one twin has been diagnosed with MS, the identical twin (from the same fertilized egg) has a 30% chance of also developing MS. Non-identical (fraternal) twins have no higher risk for MS than non-twin siblings. These findings support the results of a large-scale study in Canada which concluded that multiple cases of MS in families is "likely genetic."

As new techniques are developed to help us understand more about the role of genetics in the course of all diseases, we will surely uncover answers to many important questions about MS.

Sex and Age

MS occurs two to three times more often in women than in men. The onset of symptoms almost never occurs before puberty and reaches a peak around the age of 30. Although initial symptoms can first appear into the forties, there is a sharp decline of new cases after this age. Studies also tell us that the likelihood of developing MS is established by the age of fifteen. In fact, scientists now believe that people who are born in an area of the world with a high risk of MS and move by age 15 to an area with a lower risk, acquire the risk of their new home.

Geographic Distribution

MS geographic distribution

Recent studies have confirmed earlier suspicions that people living in certain regions are more prone to develop MS than those living in other areas. These findings gave hope to identifying a single causative factor common to geographic settings that is responsible for triggering the onset of MS. Such a discovery could potentially lead to eradicating the disease.

Unfortunately, recent data indicate that conflicting patterns of distribution are found within countries, and even within small regions. This breakthrough provided fuel for the "race-versus-place" debate in determining susceptibility for MS.


We know that Caucasians of European descent have the highest prevalence of MS in the world. Black Africans, Japanese and Chinese have an extremely low rate of MS. This rate increases for blacks living in northern America, but does not for Asians removed from their native lands. MS is thought to be nonexistent in Eskimos.

Studies of populations that have relocated to new geographic regions suggest that the "risk of MS in a single ethnic group varies with place of residence during a critical period in childhood," up to the age of fifteen.


Findings from several studies in the United Kingdom as well as the United States indicate that MS is more common in populations with higher socioeconomic status. Especially at risk are whites, and black females. Scientists speculate that in countries with warm climates and low standards of living, children may actually be exposed to MS-causing factors, but develop immunity to them.


There is no research to date that proves that MS is caused by infective organisms, but there is enough evidence to suggest a strong possibility that such a link does, in fact, exist. In recent years, medical research has discovered that viral infections might be the causative factor in such illnesses as diabetes, cancer, and AIDS. Some neurologists now believe that MS may arise from both a virus and an autoimmune response.

Researchers suspect that MS may somehow be related to the virus that causes canine distemper. A study in the 1970's revealed that people who had, at some time in their lives, owned a small dog were more likely to develop MS. A later study conducted in the Orkney Islands just off the coast of Scotland, where the incidence of MS is unusually high, the occurrence of MS was even higher during World War II when soldiers returned home with their dogs. Years later, when the dog population declined and the rate of canine distemper decreased the number of new cases of MS also decreased.