[1] Royal Free Hosp, Sheila Sherlock Liver Ctr, London NW3 2QG, England
[2] UCL, Royal Free Sheila Sherlock Liver Ctr, London, England
[3] UCL, Univ Dept Surg, London, England
[4] Univ Catania, Garibaldi Hosp, Catania, Italy
[5] Osped Cervello Palermo, Gastroenterol Unit, Palermo, Italy
[6] Univ Milan, Inst Med Stat & Biometry, Milan, Italy