Clinical implications of inflammatory bowel disease genetics on phenotype

The genetic revolution has been with us for over a decade now. We have yet to see this impacting the care of patients except in a few rare examples. However, progress has been made in the field of inflammatory bowel disease (IBD) that could soon be translated to the bedside, both in terms of predicting the disease course as well as in the response to therapy. IBD traditionally has been classified as ulcerative colitis and Crohn's disease, with 10% of patients classified as having indeterminate colitis on the basis of clinical, radiologic, endoscopic, and histologic findings. However, this traditional view is now being challenged. Developments in genetics and serological markers, as well as an appreciation of the disease course, have led to an understanding that IBD is a heterogeneous group of diseases with some common genetic and environmental factors but different clinical manifestations in terms of disease behavior, location, and response to treatment. Data are now emerging that may allow us to more objectively select the correct therapy for the correct patient, rather than the current approach, which is based on clinical experience backed up by a less-than-perfect evidence base. In this article, we will review the evidence for this.