Abstract

It is now clear that the major identified risk factor for the inflammatory bowel diseases (IBDs) is a positive family history. Furthermore, the available data in spouses and twins indicate that the genetic susceptibility is due in large measure to shared familial predisposition. This emphasizes the importance of identifying the actual familial susceptibilities. Given the data for immunopathogenetic etiologies in the genesis of IBD, the logical candidate genes are those that involve the immune system. Data for several of these gene marker systems have been considered confusing or inconclusive. When approached with the concept that IBD is a genetically heterogeneous group of disorders, patterns are beginning to emerge for the human lymphocyte antigen class II region genes on chromosome 6, and the complement C3 gene on chromosome 19. Available data do not yet implicate the immunoglobulin or T cell receptor genes, but further studies are needed, especially for the latter. Firm identification of genetic susceptibilities will require the study of an adequate number of families, which is being facilitated by the establishment of an IBD family-based cell line bank. Identification of the genes that predispose to IBD will allow the study of natural history from susceptibility to clinical disease and, when understood, will provide new approaches to disease therapy and even prevention.