1. Department of Gastroenterology and Hepatology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands
2. Department of Epidemiology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands
3. Department of Genetics, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands
4. Department of Medical Microbiology, University of Groningen and University Medical Center Groningen, Groningen, The Netherlands