1Departments of Gastroenterology, Peking University First Hospital, Beijing, China.
Correspondence: Huahong Wang. E-mail: firstname.lastname@example.org.
Received December 13, 2018
Accepted March 14, 2019
Online date: May 31, 2019
This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.