The cell surface glycoprotein known as the cellular prion protein (PrPC) has been the subject of intensive study since it was first proposed that misfolding of PrPC plays a key role in the pathogenesis of the neurodegenerative disorders referred to as either the transmissible spongiform encephalopathies (TSEs) or prion diseases (Prusiner, 1982). Here, PRNP is linked to human prion disease.