Editorial: in search of environmental risk factors of Crohn's disease and ulcerative colitis with mendelian randomisation-authors' reply.

Address: Department of Gastroenterology, The Third Xiangya Hospital, Central South University, Changsha, China.; Centre for Global Health, Zhejiang University School of Medicine, Hangzhou, China.; Department of Big Data in Health Science, School of Public Health and The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, China.; Unit of Cardiovascular and Nutritional Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.; Centre for Global Health, Usher Institute, University of Edinburgh, Edinburgh, UK.; Cancer Research UK Edinburgh Centre, Medical Research Council Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, UK.; Translational Gastroenterology Unit, Nuffield Department of Medicine, Experimental Medicine Division, John Radcliffe Hospital, University of Oxford, Oxford, UK.