[1] Inst Neurol, Dept Neurodegenerat Dis, London WC1N 3BG, England
[2] Inst Neurol, MRC, Prion Unit, London WC1N 3BG, England
[3] Natl Inst Med Res, London NW7 1AA, England
[4] Queen Marys Sch Med, Barts & London, Inst Cell & Mol Sci, Ctr Haematol, London E1 2AT, England
[5] Newcastle Univ, Inst Human Genet, Int Ctr Life, Newcastle Upon Tyne NE1 3BZ, Tyne & Wear, England
[6] Guys Hosp, Univ London Kings Coll, Dept Craniofacial Dev, London SE1 9RT, England