PRNP and prion disease: Although increased levels of C2 fragments occur in prion disease states (Chen et al, 1995; Yadavalli et al, 2004; Dron et al, 2010) and mice programmed to express a C2 fragment develop a spontaneous disease syndrome (Colby et al, 2010), we were unable to detect spontaneous neurological disease in TgPrP(S1) and TgPrP(S3.F88W) mice at nearly 2 years of age, nor the presence of a PK-resistant PrP species by Western blot of brain homogenates from these mice (Supplementary Table S1).