Transmission of vCJD prions to Tg27 mice resulted in only 2/11 clinical attack rate with prolonged incubation periods greater than 482 days post-inoculation (Table 2), but 11/11 total infection rate (positive either by clinical scoring, immunoblot or immunohistochemistry), mirroring transmission properties of the same vCJD inoculum in homozygous human PrP 129MM-expressing Tg35 and Tg45 mice (Asante et al., 2002). This evidence concerns the gene PRNP and variant Creutzfeldt-Jakob disease.