Medical text and Psychological and behavioural characteristics text written June 1997 by Dr A Barnicoat, Consultant in Clinical Genetics, Institute of Child Health, London, UK and Professor J Turk. Last updated December 2005 by Professor J Turk, Professor of Developmental Psychiatry and Consultant Child & Adolescent Psychiatrist, Department of Clinical Developmental Sciences, St. George's Hospital Medical School, London, UK.