From Hippocrates’ Shadow, by David Newman:
Why does Bennington have one of the highest MS rates in the world? We don’t know, but we can read the maps that show it to be true. Studies of epidemiologic trends have established that the highest incidence of MS rests firmly at this latitude, 40 degrees or greater, throughout much of the industrialized world. If you’re born in northern Wisconsin, or in the Scottish Highlands, or in New Zealand at latitude that’s 40 degrees or more from the equator, your likelihood of developing MS is strikingly similar to that of people born in Bennington, Vermont.
Reference 3 is:
3. Hammond, S. R., J. G. McLeod, K. S. Millingen, et al. 1988. The epidemiology of multiple sclerosis in three Australian cities: Perth, Newcastle and Hobart. Brain 111: 1–25; Kuroiwa, Y., H. Shibasaki, M. Ikeda. 1983. Prevalence of multiple sclerosis and its north–south gradient in Japan. Neuroepidemiology 2: 62–69; Kurtzke, J. F., G. W. Beebe, J. E. Norman. 1979. Epidemiology of multiple sclerosis in U.S. veterans. I. Race, sex and geographic distribution. Neurology 29: 1228–35; Skegg, D. C., P. A. Corwin, R. S. Craven, J. A. Malloch, M. Pollock. 1987. Occurrence of multiple sclerosis in the north and south of New Zealand. J Neurol Nerosurg Psychiatry 50: 134-39.