PRNP and scrapie: The majority of normal PrP is known to be expressed as a GPI-linked cell surface glycoprotein, and surprisingly, in transgenic mice expressing PrP devoid of GPI anchoring, a classical prion strain (RML scrapie) does not induce clinical disease despite the presence of amyloid PrPres and replication of scrapie infectivity (Chesebro et al., 2005).