The most common form of human TSE is sporadic Creutzfeldt-Jakob disease (CJD) which has six main clinical subtypes correlating with the methionine/valine polymorphism at codon 129 of the PRNP gene and the size of un-glycosylated isoform of present PrPTSE (MM1, MM2, MV1, MV2, VV1, VV2). Here, PRNP is linked to human prion disease.