1. Department of Chemical Pathology, The National Hospital, Queen Square, London WC1N 3BG, Chalfont Centre for Epilepsy, Chalfont St Peter, Gerrards Cross, Buckinghamshire SL9 ORJ
2. Wexham Park Hospital, Slough SL2 4HL, UK
3. Department of Chemical Pathology, The National Hospital, Queen Square, London WC1N 3BG