We are indebted to the IDEAL principal investigators, the study coordinators, nurses and patients involved in the study. We also recognize E. Gustafson, P. Savino, D. Devlin, S. Noviello, M. Geffner, J. Albrecht and A. C. Need for their contributions to the study. This study was funded by Schering-Plough Research Institute, Kenilworth, New Jersey. A.J.T. received funding support from the National Health and Medical Research Council of Australia and the Gastroenterological Society of Australia.

Author Contributions D.G., J.F., A.J.T. and J.S.S. contributed equally to this work. D.G., J.F. and A.J.T. performed the statistical and bioinformatical analyses. J.F. and A.J.T. defined the clinical phenotypes. K.V.S. performed the genotyping. D.B.G. and D.G. drafted the manuscript. J.S.S., J.G.M. and D.B.G. designed the study. All authors collected and analysed data and contributed to preparing the manuscript.