PRNP and sporadic Creutzfeldt-Jakob disease: Reflecting this evidence, the current histo-molecular classification of sporadic Creutzfeldt-Jakob disease (sCJD), the most common human prion disease, largely relies on the association between a host polymorphism at PRNP codon 129 (coding for methionine/M or valine/V), and two distinct types of the disease-related prion protein (PrPSc type 1, and type 2) differing in the molecular mass of their protease-resistant fragment [21, 25].