Consequently, we have found that demonstration of vCJD prion transmission to human PrP 129M mice is most reliably determined by demonstrating the propagation of type 4 PrPSc in the brain of inoculated recipients by immunoblotting rather than measuring the incidence and timing of clinical prion disease [7,8,24,25,31]. The gene discussed is PRNP; the disease is variant Creutzfeldt-Jakob disease.