Allow me to start, but I will toss it to Dr. Marrie.
I like to describe MS as a perfect storm. What we do know is that it's a complex disease. There are 230 genetic loci that have been identified and are associated with the disease, and then if you stack on top of that environmental circumstances over the life-course of an individual and it is that perfect storm, then you tend to see the expression of the disease.
What we know today is we could identify it much earlier—in fact years earlier—than we probably can today. We don't really know why Canada has the highest rates in the world, but it's likely a combination of those factors of genetic predisposition and environmental circumstances that has led to that. If you look around the world, there's a northern country band, a latitude band of the kinds of countries that have the highest rates in the world.
I ask Dr. Marrie to comment as well.