Relationship between site of disease and familial occurrence in Crohn's disease

Concordance in the extent of disease among thefamily members of patients with Crohn's disease has notbeen widely investigated. Furthermore, the relationshipbetween the site of the disease and familial occurrence has never been studied. Our aim wasto evaluate the familial occurrence of Crohn's diseasein the various sites. Nine hundred thirty-four patientswith Crohn's disease, observed consecutively in two gastrointestinal departments, wereinvestigated to determine first-degree familialincidence (in both Crohn's disease and ulcerativecolitis). Whenever two or more members were attendingthe same clinic, only one was regarded as a propositus.The analysis, therefore, was carried out on 882patients. The exact site of the disease was determinedin all patients either at diagnosis or during thefollow-up by colonoscopy and by small bowel enema. Therate of concordance in the extent of disease andfamilial occurrence in the various sites was evaluatedand the difference was calculated by chi-square test. Sixty-one propositi were identified among allthe patients. Forty-nine had familial occurrence for thesame disease (concordant patients), whereas 12 had atleast one relative with ulcerative colitis (discordant patients). In 44 propositi with only onerelative affected, the rates of concordance in theextent of the disease were 84, 68, 18, and 0%respectively, for the ileum, the ileum-right colon, theileum-total colon, and the colon. The number of propositiin the various sites was as follows: 4 of 162 (2.4%)patients with the disease located in the colon, 1 of 9(11%) with the jejunum site, 24 of 380 (6.3%) with the ileum site, 16 of 165 (9.7%) with the ileumand right colon site, and 16 of 164 (9.7%) with theileum and total colon site. The chi-square values ofpropositi distribution among other sites and the colon was, respectively, as follows: jejunum,2.2 (N.S.); ileum, 3.4 (P = 0.06); ileum and rightcolon, 7.4 (P = 0.006); and ileum and total colon, 7.4(P = 0.006). This study shows a pronounced concordancein the site of the disease for family members withCrohn's disease and suggests that familial occurrence inCrohn's disease is less frequent when the disease islocated in the colon rather than elsewhere.