Footnotes

• Contributors This review is based on an invited talk given by KWO at the British Society of Gastroenterology Annual Meeting in June 2019. NB and KWO drafted the manuscript and approved the final version. KWO submitted the review and is guarantor for the overall content.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Patient consent for publication Not required.

• Provenance and peer review Not commissioned; externally peer reviewed.