We proposed a classification of sporadic human prion diseases based on the pairing of the patient’s genotype at codon 129 of the PrP gene (the site of a common methionine (M)/valine (V) polymorphism) with the type, 1 or 2, of PrPSc (as determined by electrophoretic mobility of the protease resistant PrPSc core or resPrPSc)11, 12. This evidence concerns the gene PRNP and prion disease.