Its conversion into a partly protease-resistant, β-sheet-rich misfolded isoform, called PrPd under a generic term (disease-linked prion protein), and its accumulation in aggregative forms in the CNS are hallmarks of fatal neurodegenerative disorders that are known for decades as transmissible spongiform encephalopathies, or prion diseases (Gajdusek, 1977; Prusiner, 1991). Here, PRNP is linked to prion disease.