Competing interests: AC reports grants from the Wellcome Trust and royalties from Elsevier all outside the submitted work. VM reports personal speaker fees from Takeda UK, and meeting and travel grants from Dr Falk Pharma (UK), Janssen-Cilag, Takeda UK, all outside the submitted work. CS reports consulting fees from Ferring, personal speaker fees from Takeda, Janssen, Abbvie, Tillotts, Norgine, Fresenius Kabi, meeting and travel grants from Tillots, Abbvie, Janssen, and advisory board fees from Galapagos, AbbVie, Arena, Janssen, Fresenius Kabi all outside the submitted work. CL reports grants from Genentech, grants and personal fees from Janssen, grants and personal fees from Takeda, grants from AbbVie, personal fees from Ferring, grants from Eli Lilly, grants from Pfizer, grants from Roche, grants from UCB Biopharma, grants from Sanofi Aventis, grants from Biogen IDEC, grants from Orion OYJ, personal fees from Dr Falk Pharma, grants from AstraZeneca, outside the submitted work. IP reports speaker fees from Olympus, Boston Scientific, and Dr Falk outside the submitted work. SD reports grants from The Helmsley Charitable Trust, Edinburgh and Lothians Health Foundation, Pathological Society of Great Britain and Northern Ireland, Lord Leonard and Lady Estelle Wolfson Foundation, consulting fees from Abbvie, personal speaker fees from Janssen and Takeda, and meeting and travel grants from Janssen, Takeda and Dr Falk, all outside the submitted work.