PRNP and prion disease: The permissiveness of bank vole PrPC is well known (15,16,18,21–27); it is exemplified by the observation that, despite the mere 8-aa PrPC divergence between bank voles and mice, a variety of human and animal prion diseases not transmissible to mice are infectious to bank voles and transgenic mice expressing bank vole PrP (15,16,18,22,24).