In the prion theory of Prusiner [1] transmissible spongiform encephalopathies are proposed to be caused by a proteinaceous infectious agent, a pathological variant of the normal cellular prion protein, PRNP scrapie (PRNPSc; also named PrPSc), which acts as a template for the conversion of normal cellular prion protein PRNPC (also named PrPC) to PRNPSc. Here, PRNP is linked to human prion disease.