1. Department of Neurodegenerative Disease, Institute of Neurology, Queen Square, London WC1N 3BG, UK.
2. Medical Research Council Prion Unit, Institute of Neurology, Queen Square, London WC1N 3BG, UK.
3. National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK.
4. Centre for Haematology, Institute of Cell and Molecular Science, Barts and The London, Queen Mary's School of Medicine, 4 Newark Street, London E1 2AT, UK.
5. Institute of Human Genetics, University of Newcastle upon Tyne, International Centre for Life, Central Parkway, Newcastle upon Tyne, NE1 3BZ, UK.