PRNP and Creutzfeldt Jacob disease: Previous studies using post-mortem human brain extracts demonstrated that the disease-associated PrP in Creutzfeldt–Jakob disease (CJD) brains is cleaved by a cellular protease to generate a C-terminal fragment, referred to as C2, which has the same molecular weight as PrP27–30, the protease-resistant core of PrPSc (Chen et al., 1995).