Epidemiology of inflammatory bowel disease.

Epidemiologic studies of inflammatory bowel disease indicate that these disorders occur in susceptible individuals, possibly due to genetic abnormalities, resulting in disturbance of bowel wall function. Environmental factor(s) exerting a primary effect at an early age, in most patients, cause the disease to manifest usually in teenagers or young adults. Secondary environmental factors may alter disease expression, severity, or influence relapse. Studies in identical twins provide the best evidence for the role of genetic factors in the cause of Crohn's disease. Changing trends in disease incidence (seen in many countries) provide strong support for environmental factors as playing a major influence in disease expression. We now require further laboratory and epidemiologic studies in family members at risk of disease, in migrants who move from low incidence areas to high incidence areas, and in area where Crohn's disease particularly is starting to appear. The clinician can play an important role by performing careful observations in patients with a view to uncovering new clues to disease etiology.