1. The Netherlands Foundation for the Detection of Hereditary Tumours, Leiden, The Netherlands
2. Department of Gastroenterology, Leiden University Medical Centre, Leiden, The Netherlands
3. Second Department of Surgery, University Central Hospital, Helsinki, Finland
4. Swedish Polyposis Registry, Department of Gastroenterology and Hepatology, Karolinska Hospital, Karolinska Institute, Stockholm, Sweden
5. Mount Sinai Hospital, Familial Gastrointestinal Cancer Registry, Toronto, Canada