Etiology of the inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are complex disorders. While the exact et iology of these diseases remains unknown, recent progress in the epidemiolo gy and genetics of IBD has clearly demonstrated both environmental and gene tic factors to play a role in the development of the disease, and it is exp ected that some risk factors are common for both Crohn's disease (CD) and u lcerative colitis (UC). The environmental factor(s) are associated with the Western way of life in the second half of the twentieth century. Cigarette smoking is presently the best known environmental factor. However, the eff ect of tobacco is opposite in CD and UC. A familial history of IBD is the m ost important risk factor for developing the disease, suggesting a genetic predisposition to IBD. This hypothesis has recently been confirmed by the l ocalization of at least two susceptibility loci on chromosomes 12 and 16. T hese genes seem to play a role in both CD and UC. They must now to be ident ified.