PRNP and Creutzfeldt Jacob disease: The Creutzfeldt-Jakob disease (CJD) with 13-kDa fragments, e.g., sporadic CJD with methionine homozygosity at the codon 129, showed shortened incubation periods in human-mouse chimeric PrP-expressing mice, corroborating the significance of structural variation in strain barriers of PrPSc prions [36,43].