Empirical evidence for this came from Parchi et al. (2000) who showed that codon 129 is a primary determinant of the proteinase cleavage site of PrPSc in CJD, resulting in a change in the size of the PrP proteinase resistant fragments (Parchi et al., 2000). The gene discussed is PRNP; the disease is Creutzfeldt Jacob disease.