PRNP and prion disease: Prion diseases are a group of neurodegenerative diseases caused by the conversion of the normal form of prion protein (PrPC, prion-related protein, in which C stands for the cellular form of the protein) with a primarily alpha-helical structure into an abnormal form of the prion protein (PrPSc, proteinaceous infectious particle, in which Sc stands for scrapie, the prion disease of sheep and goats), which has a primarily beta-pleated sheet structure.