Inflammatory bowel disease. An epidemiological and genetic study.

The epidemiology of ulcerative colitis (UC) in Stockholm County over a 25-year period, 1955-1979, was investigated. There were 1,274 cases--681 males and 593 females. The proportion of patients with proctitis, left-sided, and total extent of disease remained constant over the study period, as did the time interval between onset of symptoms and definite diagnosis. The incidence increased over the first 20 years followed by a plateau and was 4.3 per 10(5) inhabitants at the end of the study period. The peak incidence in relation to age increased, but remained in the 3rd and 4th decade throughout the study period. In a population-based study of UC the overall prevalence of extracolonic diagnoses was 21%. Seventy percent of patients with extracolonic diagnoses had extensive colitis whereas among the patients without extracolonic diagnoses only 28% had extensive colitis (p less than 0.001). The extracolonic diagnoses were classified into two major groups, activity-related and autoimmune, the former is related to the extent and activity of UC and responds to both medical and surgical treatment, whereas the latter is unaffected by medical and surgical treatment for UC. A total of 364 diagnoses were distributed among 271 UC patients. The prevalence of extracolonic diagnoses was higher in familial UC (p less than 0.05), but was distributed as UC in general mostly with activity-related diagnoses. The familial occurrence of inflammatory bowel disease (IBD) was investigated among 963 patients with UC. There was a general prevalence of 7.9% for familial IBD. In 80% one relative was affected, in most cases this was a first degree relative with UC. Sibship was the most common relationship. No concordance for UC was found among three pairs of monozygotic twins. The prevalence of UC in first degree relatives of index patients was 15 times higher than in non-relatives. The age at onset was significantly lower among patients with a family history for UC; they also had a higher prevalence of total colitis. The prevalence of Crohn's disease (CD) in first degree relatives of index patients with UC was almost 3.5 times higher than in non-relatives. Complex segregation analysis of 124 families with UC where two or more individuals were affected points to a rare additive major gene with a low penetrance as the cause of the disease with. About 20% of the affected were heterozygotes for the gene. There was no evidence for multifactorial inheritance. The prevalence of IBD was found to be 13.4% in a population-based study on patients with CD.(ABSTRACT TRUNCATED AT 400 WORDS)