GENETICS AND EPIDEMIOLOGY OF INFLAMMATORY BOWEL DISEASES

Inflammatory bowel diseases (IBD) have been reported throughout the wo rld, but their frequency is highest in Northern Europe and the USA. Th e mean incidence of ulcerative colitis is 6/10(5) inhabitants, and tha t of Crohn's disease is 4/10(5) inhabitants. Inflammatory bowel diseas es occur in young adults, especially Crohn's disease which reachs a pe ak of incidence between 20 and 30 years. Among possible factors influe ncing their incidence, only tobacco smoking has been shown to facilita te the acute episodes and relapses of Crohn's disease and to diminish those of ulcerative colitis. The frequency of familial inflammatory bo wel diseases, which mainly affects first degree relatives, varies from 6 to 36 %. A genetic component is present and probably more important for Crohn's disease than for ulcerative colitis, although no genetic marker has yet been identified