PRNP and Ataxia: Specifically, Nagasaki (Ngsk) and Rcm0 Prnp-deficient mice develop ataxia in old age, due to cerebellar Purkinje cell degeneration (Sakaguchi et al., 1996; Moore et al., 1999; Prestori et al., 2008), whereas the other lines; i.e., Zürich I and Edinburgh (Edbg) Prnp-deficient mice, never exhibit this abnormal phenotype (Büeler et al., 1992; Klamt et al., 2001).