PRNP and human prion disease: Prion diseases (PDs), or transmissible spongiform encephalopathies (TSEs), are fatal, progressive neurodegenerative disorders characterized by the accumulation, in the central nervous system (CNS) as well as in peripheral nervous and extraneural tissues, of a pathological isoform, PrPSc, of the host-encoded, cellular prion protein (PrPc) [7].