Canada has one of the highest rates of multiple sclerosis in the world, according to an international survey.

Gael Hepworth holds her dog Gregory in her Toronto home. Hepworth suffers from multiple sclerosis and attends a support group which provides therapy to help people deal with the emotional aspects of having a chronic illness. (Chris Young/Canadian Press)The 2008 Atlas of Multiple Sclerosis showed MS strikes 133 out of every 100,000 people in Canada, the fifth highest rate among countries surveyed between 2004 and 2005.

Prevalence was higher in the United States, Germany, Norway and Hungary, according to the World Health Organization and the Multiple Sclerosis International Foundation, which published the report.

The MS Society of Canada says the rate of MS in this country could be as high as 240 per 100,000 people.

Some people with MS experience little disability during their lifetime. But up to 60 per cent are no longer fully able to walk 20 years after onset, which has major implications for their quality of life and costs to society, the report said. Symptoms appear around 30 years of age on average.

"The Atlas of MS reveals how these implications impact women more than men, by at least two to one, at an age when they are starting a family and developing a career," said Dr. Benedetto Saraceno, director of the WHO's department of mental health and substance dependence.

Canada has been a leader in terms of diagnosing, treating and working to improve the quality of life of people with MS. But keeping people with MS employed remains a challenge, the Multiple Sclerosis Society of Canada said.

Canadian women are more than twice as likely to get multiple sclerosis than men, according to a major study published in November 2006. Among those born in the 1930s, about two women contracted MS for every one man, at a ratio of 1.9 to 1. For those born in the 1980s, the incidence has grown to exceed 3.2 cases for every one case among men.

Why the sudden increase in the neurodegenerative disease, which attacks the brain and spinal cord, causing inflammation and damage that can lead to paralysis and sometimes blindness?

We don't know. We don't know what causes MS. We don't know what cures MS. The whys and wherefores of this mysterious disease have bedevilled scientists, health-care workers and victims for nearly 200 years.

Recent speculation about the cause has ranged from genetics to environment to vitamin deficiencies to even the birth control pill.

An Italian vascular surgeon — Dr. Paolo Zamboni of the University of Ferrara — has been exploring the theory that MS is caused by blocked veins in the neck or chest, preventing blood from draining properly from the brain. He has developed a surgical technique to treat the problem.

A team at the University of Buffalo — led by Dr. Robert Zivadinov, who worked on an earlier study with Zamboni — has recruited hundreds of patients in Canada and the U.S. to explore the theory further. The patients will undergo specialized neck scans to look for narrowed veins.

MS rates higher in northern lattitudes

Health officials consider a country to have a "high" rate if they have more than 30 cases per 100,000.

The incidence among the provinces varies, from a high of 340 cases for every 100,000 people in the Prairies to a low of 180 cases per 100,000 in Quebec, according to a 2005 study by researchers at the University of Calgary.

Those aged 15 to 40 are most at risk. One out of every two Canadians know someone with MS.

People who live closest to the equator have the lowest incidence of MS.

However, that doesn't explain why the disease is nearly absent among Canada's Inuit in the High Arctic and among indigenous people in North America and Australia, or why it is rarely found in Japan.

Study suggests MS is environment-based, preventable

The study on the rising incidence of women with MS was done by a team of researchers led by George Ebers, a professor of neurology at the University of Oxford. It appears in the November 2006 issue of the journal Lancet Neurology.

The higher incidence of MS among women may not be bad news, according to the researchers — because it may help to shed light on what causes the disease.

"What is going on here is something presumably that is preventable," said Ebers, who was the lead author of the study.

"We just need to find out what it is in the environment. Because it has to be in the environment: your genes don't change over two generations, three generations."

Higher estrogen levels, less sunlight blamed

There has also been speculation that because MS is generally more prevalent in colder climates far north of the equator and far south of the equator, it may be due to vitamin D deficiencies.

The body produces the vitamin in response to sunlight and so vitamin D levels fall off in colder countries and in winter because the sun's rays aren't intense enough.

Because of the rising incidence of MS among women and because it seems to have started in the 1960s, many others have speculated that the cause may be connected to higher levels of the hormone estrogen due to the introduction of the birth control pill.

But Ebers, who spent 22 years at the University of Western Ontario in London, Ont., before going to Oxford, rejects these factors as likely explanations.

"I think one of the things one thinks of here is either that it's going to be something in the environment or it is going to be an environmental interaction with genes."