Rare acquired forms of CJD caused by human to human or animal to human transmission of infectious prions [74], and atypical disease variants with a slower progression, such as Gerstmann-Sträussler-Scheinker syndrome (GSS), prion protein-cerebral amyloid angiopathy (PrP-CAA) and variably protease-sensitive prionopathy (VPSPr) complete the phenotypic spectrum of human prion diseases of the CNS [25, 81]. This evidence concerns the gene PRNP and Gerstmann-Straussler-Scheinker syndrome.