Medical text written November 1991 by Contact a Family. Approved November 1991 by Professor M Patton, Professor of Medical Genetics, St Georges Hospital Medical School, London, UK and Dr J E Wraith, Consultant Paediatrician, Royal Manchester Children’s Hospital,UK. Last updated June 2004 by Dr Mike Wolfman, General Practitioner and Secretary to the Professional Panel, Williams Syndrome Foundation, Tonbridge, UK. Psychological and behavioural characteristics last reviewed January 2004 by Dr Orlee Udwin, Consultant Clinical Child Psychologist, West London Mental Health NHS Trust, London, UK.