[Epidemiology, risk factors and factors associated with disabling course in inflammatory bowel disease]

Inflammatory bowel diseases (IBD) are not rare and would affect near of 5 million of patients in the world (including 2.5 in North America and 2.5 in Europe with at least 200,000 in France). These are chronic relapsing disorders affecting young patients (peak of incidence in patients aged from 20 to 30 years), particularly the young females (sex ratio F/M: 1.3). Their cause is unknown and there is no curative treatment. Although many research studies have isolated more than 160 genes whose variants are associated with these diseases, the weight of genetics remains low in their occurrence. Significant time and space variations in incidence of IBD have been reported. Firstly, an increase of IBD incidence has been reported overtime worldwide. Secondly, a space variation in IBD incidence has been noted with a dramatic increase in emerging countries. Even within a same geographical area through a prospective population-based dataset since 27 years (EPIMAD Registry), a spatial heterogeneity of incidence has been reported, suggesting the important role of the environment in the occurrence of these diseases. Smoking and appendectomy are the only environmental factors clearly involved in the development and progression of IBD and cannot explain spatial and temporal heterogeneity in the IBD observed incidence worldwide. New multidisciplinary basic and epidemiological studies are needed to identify the factors involved in the onset of IBD.