Editor,—I was interested to read the review on the role of inherited factors in inflammatory bowel disease by Satsangi et al (Gut1997;40:572–4), but dismayed by the evidence provided. They claim that twin pairs provided strong evidence for genetic predisposition and that the most pertinent was that reported by Tysket al using data from the Swedish Twin Registry.1 However, the claim for ulcerative colitis rests on a single twin of the 50 000 registered. The probands were identified as hospitalised cases in Sweden. The 50 pairs of twins where one twin had suspected ulcerative colitis were whittled …