Multiple sclerosis: does epidemiology contribute to providing etiological clues?

The epidemiological approach has undoubtedly contributed to our knowledge of Multiple Sclerosis (MS) by providing some etiological hypotheses in spite of the fact that a definitive basis for the conclusive resolution of its enigma is still lacking. Epidemiological studies have indicated that MS has an uneven geographical distribution and a changing incidence over time at least in several areas of the world: this suggests an etiological role of both genetic and environmental factors. The racial difference in disease risk, the results of familial and twin studies as well as the association between MS and some HLA markers, support the great importance of genetic factors. On the other hand, the evidence of temporal trends and the data from migrant studies seem to underline the etiological contribution of environmental factors. In the light of these results much of the present views have emerged interpreting the disease as caused by multiple factors acting at a susceptible age in genetically predisposed subjects.