PRNP and prion disease: In order to determine whether or not the PrPSc allotype ratio influenced the transmission properties of MV heterozygous cases of CJD, brain samples from 10 cases of codon 129 heterozygous sCJD (n = 7) or iCJD (n = 3) whose prion disease phenotype had been previously characterized both neuropathologically and biochemically [28], were tested for their ability to transmit disease to transgenic mice overexpressing human PrPC-M129.