Prevalence and family risk of ulcerative colitis and Crohn's disease: an epidemiological study among Europeans and south Asians in Leicestershire.

The family history of patients identified during incidence studies in Leicestershire were investigated and the prevalence and comparative risks calculated; 1254 patients aged 15 to 80 years were sent a questionnaire about their family history. All cases with a positive family history were reviewed and confirmed cases included in the study. In Europeans the standardised prevalence of Crohn's disease was 75.8/10(5) and that of ulcerative colitis 90.8/10(5). The prevalence of Crohn's disease among South Asians was 33.2/10(5) and that of ulcerative colitis 135/10(5). The prevalence of Crohn's disease in Europeans was significantly greater than that in Hindus (chi 2 = 16, p < 0.001), while the prevalence of ulcerative colitis was significantly lower in Europeans than Hindus (chi 2 = 27, p < 0.001) and Sikhs (chi 2 = 4.4, p < 0.05). The comparative risk of developing ulcerative colitis in first degree relatives of Europeans patients with ulcerative colitis was increased by approximately 15, but the risk of Crohn's disease was not increased. The comparative risk of developing Crohn's disease among first degree relatives of patients with Crohn's disease was increased by up to 35, the comparative risk of ulcerative colitis was approximately 3. The risk among relatives of South Asian patients with Crohn's disease was not increased, but the risk of ulcerative colitis to relatives of patients with ulcerative colitis was. This study supports the view that Crohn's disease and ulcerative colitis arise in people with a genetic predisposition and exposed to some, as yet unknown, environmental factor.