1 The Polyposis Registry, St Mark's Hospital, Harrow, HA1 3UJ, United Kingdom. Electronic address: guihanlee@nhs.net.
2 The Polyposis Registry, St Mark's Hospital, Harrow, HA1 3UJ, United Kingdom; Department of Paediatric Polyposis, St Mark's Hospital, Harrow, HA1 3UJ, United Kingdom.
3 The Polyposis Registry, St Mark's Hospital, Harrow, HA1 3UJ, United Kingdom.