Epidemiology and genetics

Multiple sclerosis is not evenly distributed throughout the world. For many years, it had been suggested that the prevalence of MS, in Europe in particular, was directly related to latitude: the further from the equator, the more common the disease. However, wide variations in prevalence between geographical areas of similar latitude prove this idea to be incorrect, except for the yet unexplained observations that Tasmania has a prevalence of MS twice that of southern Australia, despite the fact that the populations in these two areas have essentially identical ethnic origins.