Challenge of our transgenic mice expressing human PrP 129M with 129MM vCJD patient brain results in a high incidence of prion infection and faithful propagation of type 4 PrPSc (London classification, [26]) [7–9,23–25] which is pathognomonic of the vCJD prion strain [8,26,27]. The gene discussed is PRNP; the disease is variant Creutzfeldt-Jakob disease.