Within the spectrum of sporadic human transmissible spongiform encephalopathies (TSEs), there is considerable diversity of disease phenotypes. At least part of this variation is thought to be on the basis of different “strains” of prions (the infectious agent). Tissue deposition of PrP^res (the abnormal disease-associated conformation of the prion protein) is considered a hallmark of TSE pathology, and it can be visualized by Western blotting typically as three bands depicting the diglycosylated, monoglycosylated, and unglycosylated species. It is the mobility of the unglycosylated PrP^res, and the relative abundance of the two glycosylated bands, along with the prion protein gene (PRNP) codon 129 genotype, that seem to correlate with distinct clinico-pathological profiles of sporadic Creutzfeldt-Jakob disease.