Medical text written December 1996 Professor M Patton, Professor of Medical Genetics, St George’s Hospital Medical School, London, UK. Psychological and behavioural characteristics text written by Professor J Turk, Professor of Developmental Psychiatry, St George’s and the Institute of Psychiatry, University of London, London, UK. Last updated September 2007 by Professor G Evans, Professor of Medical Genetics, Regional Genetics Service, St Mary’s Hospital, Manchester, UK.