Exogeneous factors in the aetiology of multiple sclerosis

Neuroepidemiology has undoubtedly played a fundamental role in the study of multiple sclerosis (MS) by providing some aetiologic clues, although a def initive basis for the conclusive resolution of its enigma is still lacking. Epidemiological and genetic studies have indicated that MS is probably cau sed by multiple factors, both genetic and environmental, none of which is i ndividually sufficient, which appear to act before adolescence-or possibly later - in genetically susceptible individuals. This unifying hypothesis em phasizes, on the one hand, the role of a genetic-racial susceptibility and the importance of environmental factors and, on the other, a possible aetio logic heterogeneity and lack of specificity of the unknown endogenous and e xogeneous agents. In this context, several environmental factors may be inv olved in the aetiopathogenesis of MS in individuals who are susceptible to the effect of exposure to these factors. Situations or events with biologic al plausibility, such as childhood or adolescent infectious diseases, expos ures to geographic and socio-cultural factors, nutritional habits, hypersen sitivity, significant head and spinal trauma, and other factors may contrib ute, at different times, to the putative acquisition of MS, trigger its ons et, and modify its subsequent course. However, additional empirical evidenc e is needed to clarify the complex interplay of genetic and environmental f actors.