1 Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK. Electronic address: chrishawkes@msn.com.
2 Blizard Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
3 Dept of Neurology, John Hunter Hospital, University Newcastle, Australia.
4 Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
5 Department of Paediatrics (Neurology), Hospital for Sick Children, University of Toronto, Ontario, Canada.