John W Scadding1, J Allister Vale2,3. 1. 1 National Hospital for Neurology & Neurosurgery, London WC1N 3BG, UK. 2. 2 Department of Medicine, City Hospital, Birmingham, Birmingham B18 7QH, UK. 3. 3 School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK.