Medical text written November 1991 by Contact a Family. Approved November 1991 by Professor M Patton, Professor of Medical Genetics, St George's Hospital Medical School, London, UK and Dr JE Wraith, Consultant Paediatrician, Royal Manchester Children’s Hospital, Manchester, UK. Psychological and behavioural characteristics text written by Dr O Udwin, Consultant Clinical Child Psychologist, West London Mental Health NHS Trust, London, UK and Dr A Kuczynski, Child Clinical Psychologist, South London and Maudsley NHS Trust, London, UK. Last updated August 2007 by Jill Clayton-Smith, Consultant Clinical Geneticist, St Mary’s Hospital, Manchester, UK.