PRNP and prion disease: We investigated the effect of PRNP codon 129 polymorphism (which is known to alter susceptibility to prion disease and rate of disease progression) [35], age at onset and disease duration (binned in three groups: less than 100 days, longer than 200 days, or between 100 and 200 days) and found no significant difference between any of these groups (Supplementary Fig. 3a–c, online resource).