Transmission characteristics of heterozygous cases of Creutzfeldt-Jakob disease with variable abnormal prion protein allotypes

In the human prion disease Creutzfeldt-Jakob disease (CJD), different CJD neuropathological subtypes are defined by the presence in normal prion protein (PrP(C)) of a methionine or valine at residue 129, by the molecular mass of the infectious prion protein PrP(Sc), by the pattern of PrP(Sc) deposition, and by the distribution of spongiform change in the brain. Heterozygous cases of CJD potentially add another layer of complexity to defining CJD subtypes since PrP(Sc) can have either a methionine (PrP(Sc)-M129) or valine (PrP(Sc)-V129) at residue 129. We have recently demonstrated that the relative amount of PrP(Sc)-M129 versus PrP(Sc)-V129, i.e. the PrP(Sc) allotype ratio, varies between heterozygous CJD cases. In order to determine if differences in PrP(Sc) allotype correlated with different disease phenotypes, we have inoculated 10 cases of heterozygous CJD (7 sporadic and 3 iatrogenic) into two transgenic mouse lines overexpressing PrP(C) with a methionine at codon 129. In one case, brain-region specific differences in PrP(Sc) allotype appeared to correlate with differences in prion disease transmission and phenotype. In the other 9 cases inoculated, the presence of PrP(Sc)-V129 was associated with plaque formation but differences in PrP(Sc) allotype did not consistently correlate with disease incubation time or neuropathology. Thus, while the PrP(Sc) allotype ratio may contribute to diverse prion phenotypes within a single brain, it does not appear to be a primary determinative factor of disease phenotype.