PRNP and Creutzfeldt Jacob disease: A further fine tuning of the PrPSc signature associated with each CJD-associated strain has been obtained with the discovery that PrPSc aggregates include PrPres C-terminal fragments with a relative mass of about 12 and 13 kDa (PrP-CTF12/13), in addition to PrP 27–30 (Figure 1).