PRNP and scrapie: These results were consistent with the Cox proportional-hazard regression model results which showed a significant effect of serum PrPc levels on the survival period for mice inoculated with atypical scrapie (Wald test p = <0.0001 for both groups 1a and 1b), but did not suggest any effect of PrPc expression levels in the PrPres/PrPsc positive mice inoculated with classical scrapie or BSE (Wald test, p = 0.51, p = 0.09, p = 0.053 and p = 0.14 in groups 2, 3, 4 and 5 respectively).