1. School of Medicine, Jiaying University , Meizhou, Guangdong, P. R. China
2. Zhongshan School of Medicine, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China
3. Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Disease, The Sixth Affiliated Hospital, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China
4. Department of Gastroenterology, The Sixth Affiliated Hospital, Sun Yat-sen University , Guangzhou, Guangdong, P. R. China