In order to evaluate the effect of the R136S mutation in the in vitro propagation of human rec-PrPSc, human 129M 136R (wt) rec-PrP, human 129M 136S rec-PrP, and a mix of both rec-PrPs in ratio 1:1 were used as substrates for recPMCA and seeded with different dilutions of recPMCA-adapted CJD MM1 misfolded rec-PrP (10-1–10-8), and subjected to a unique 24-h round of standard recPMCA. The gene discussed is PRNP; the disease is Creutzfeldt Jacob disease.