PRNP and prion disease: In prion disease, strains made of different conformers of the pathogenic infectious prion protein (PrPSc) are often considered to have differing abilities to infect cells; this effect has been studied by using endpoint-titrated samples obtained by serial dilution (i.e., biologically cloned) to infect susceptible animals, which are then in turn scored for different neuropathological patterns of protein accumulation (151).