PRNP and prion disease: Inherited prion diseases (IPDs) are fatal neurodegenerative disorders caused by autosomal-dominant mutations in the human PrP gene (PRNP), and constitute about 15 % of all human prion disease (Collinge, 2001, 2005; Kovacs et al., 2002; Wadsworth et al., 2003; Mead, 2006).