Recent researches found that the south north gradient of the occurrence of multiple sclerosis is diminishing in the USA and doesn’t exist anymore in France.
Here are the two articles:
Alvaro Alonso, MD Miguel A. Herna ́n, MD
Temporal trends in the incidence of multiple sclerosis A systematic review
Neurology 71 July 8, 2008
Available in full text here:
Fromont A, Binquet C, Sauleau EA, Fournel I, Bellisario A, Adnet J, et al. Geographic variations of multiple sclerosis in France. Brain 2010;133:1889-99.OpenUrlAbstract/FREE Full Text http://brain.oxfordjournals.org/content/brain/133/7/1889.full.pdf
Thus the epidemiology of multiple sclerosis seems to shift toward a less intense south north gradient but in the same time an aggravation of the sex ratio, aggravating the burden that women bear in this inflammatory disease that affects the central nervous system (i.e. the central unit of our body in terms of information technologies).
This tendency opens new interests for more epidemiological studies in this field. All the more because the observational studies aiming to prove the mixed, genetic and environmental, etiology are entangled with the current migrations of populations, the mobility of young people in view of finding a job and the changes in life habits in the populations of the south such as using more protection against the sun rays.
Professor Confavreux had well depicted the stakes in this editorial:
An unchanging man faced with changing times Christian Confavreux
DOI: http://dx.doi.org/10.1093/brain/aws135 1663-1665 First published online: 24 May 2012
For the present moment multiple sclerosis etiological mechanism is an enigma and risks to remain so if researchers in the domain have no new data to crunch at the populational level.