For FFI, where the N-terminal part of PrPC (23–90) plays an important role for the conversion of protein [23], several peculiar biological characteristics have been observed: low amounts of PrPSc in the brain of affected individuals, a clear effect of the codon 129 genotype on disease onset and disease phenotype, and low transmission rates in animal experiments with very long incubation times [24, 25], when compared to genetic forms of CJD (E200K) and sporadic prion diseases [4, 26, 27]. This evidence concerns the gene PRNP and Creutzfeldt Jacob disease.