New IBD genetics: common pathways with other diseases
- 1Gastrointestinal Unit, Molecular Medicine Centre, University of Edinburgh, Edinburgh, UK
- 2Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK
- 3Inflammatory Bowel Disease (IBD) Research Group, Addenbrooke's Hospital, University of Cambridge, Cambridge, UK
- Correspondence to Dr Charles W Lees, Gastrointestinal Unit, Molecular Medicine Centre, University of Edinburgh, Crewe Road, Edinburgh EH4 2XU, UK;
Complex disease genetics has been revolutionised in recent years by the advent of genome-wide association (GWA) studies. The chronic inflammatory bowel diseases (IBDs), Crohn's disease and ulcerative colitis have seen notable successes culminating in the discovery of 99 published susceptibility loci/genes (71 Crohn's disease; 47 ulcerative colitis) to date. Approximately one-third of loci described confer susceptibility to both Crohn's disease and ulcerative colitis. Amongst these are multiple genes involved in IL23/Th17 signalling (IL23R, IL12B, JAK2, TYK2 and STAT3), IL10, IL1R2, REL, CARD9, NKX2.3, ICOSLG, PRDM1, SMAD3 and ORMDL3. The evolving genetic architecture of IBD has furthered our understanding of disease pathogenesis. For Crohn's disease, defective processing of intracellular bacteria has become a central theme, following gene discoveries in autophagy and innate immunity (associations with NOD2, IRGM, ATG16L1 are specific to Crohn's disease). Genetic evidence has also demonstrated the importance of barrier function to the development of ulcerative colitis (HNF4A, LAMB1, CDH1 and GNA12). However, when the data are analysed in more detail, deeper themes emerge including the shared susceptibility seen with other diseases. Many immune-mediated diseases overlap in this respect, paralleling the reported epidemiological evidence. However, in several cases the reported shared susceptibility appears at odds with the clinical picture. Examples include both type 1 and type 2 diabetes mellitus. In this review we will detail the presently available data on the genetic overlap between IBD and other diseases. The discussion will be informed by the epidemiological data in the published literature and the implications for pathogenesis and therapy will be outlined. This arena will move forwards very quickly in the next few years. Ultimately, we anticipate that these genetic insights will transform the landscape of common complex diseases such as IBD.
Competing interests CL has acted as a consultant to Abbott and Dr Falk, and received honoraria from Shire, Procter and Gamble, Ferring, and Schering-Plough for presentations at academic meetings. JS has acted as a consultant to Schering-Plough, Abbott, UCB, Shire and Ferring, and has on-going research support from Novartis and Genentech. JB and MP have no competing interests.
Provenance and peer review Commissioned; externally peer reviewed.