1. Department of Gastroenterology & Hepatology, Leiden University Medical Center, Leiden, the Netherlands;
2. Department of Gastroenterology & Hepatology, Isala Clinics, Zwolle, the Netherlands;
3. Department of Pathology, Leiden University Medical Center, Leiden, the Netherlands;
4. Department of Clinical Genetics, Leiden University Medical Center, Leiden, the Netherlands;
5. Department of Surgery, Elisabeth Hospital, Tilburg, the Netherlands;
6. The Netherlands Foundation for the Detection of Hereditary Tumors, Leiden, the Netherlands