ABSTRACT
The term infl ammatory bowel disease (IBD) encompasses a group of illnesses characterized by infl ammation, functional disturbance, and damage to the small bowel, large bowel, or both. Nearly a quarter of a million people in the United Kingdom live with IBD, of whom two-thirds have a diagnosis of ulcerative colitis (UC) and one-third have Crohn’s disease (CD). The incidence of UC is fairly stable, but there has been a steady increase in the number of CD cases over the last couple of decades. IBD is much more common in developed counties and in the Northern Hemisphere, and Ashkenazi Jews have the highest prevalence of CD in the world. Smokers are three times more likely to develop CD than nonsmokers but half as likely to develop UC; the reasons for the differential effects of smoking remain poorly understood (1) . IBD also runs in families, and there is a 10-fold increased risk if there is any family history and a 30-fold increased risk if a sibling has IBD. Fifty percent of identical twins are concordant for CD, indicating a high, but not exclusively, genetic etiology.
