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 J E Wraith, Consultant Paediatrician, Royal Manchester Children's Hospital, Manchester, UK. Last updated February 2006 by Dr A MacGregor, Director of Clinical Research, The City of London Migraine Clinic, London, UK.