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. Last reviewed July 2006 by Dr R Stanhope, Consultant Paediatric Endocrinologist, The Portland Hospital, London, UK.