A similar tissue-specific segregation of prion substrains due to distinct tropism was observed on transmission of a human vCJD case to transgenic mice overexpressing human PrP [22], on transmission of cortical MM2-sporadic CJD to tg338 mice [28], directly in a sporadic CJD individual [50] and in CWD-infected elk [51]. This evidence concerns the gene PRNP and Creutzfeldt Jacob disease.