A novel mechanism of phenotypic heterogeneity in Creutzfeldt-Jakob disease

One of remarkable features of sporadic Creutzfeldt-Jakob disease (sCJD) is the great phenotypic variability. Understanding the molecular basis of this variability has important implications for the development of therapeutic approaches. It is well established that, in many cases, phenotypic heterogeneity of sCJD is under control of two determinants: the genotype at the methionine (M)/valine (V) polymorphic codon 129 of the human prion protein gene and the type, 1 or 2, of the pathogenic and disease-related form of the prion protein, PrP^D. However, this scenario fails to explain the existence of distinct heterozygous sCJDMV2 subtypes, where heterogeneity occurs without any variation of the 129 allotype and PrP^D type. One of these subtypes, denoted sCJDMV2C, associated with PrP^D type 2, is characterized by widespread spongiform degeneration of the cerebral cortex (C). The second variant, denoted sCJDMV2K, features prominent deposition of PrP^D amyloid forming kuru type (K) plaques. Here we used a mass spectrometry based approach to test the hypothesis that phenotypic variability within the sCJDMV2 subtype is at least partly determined by the abundance of 129 M and 129 V polymorphic forms of proteinase K-resistant PrP^D (resPrP^D). Consistent with this hypothesis, our data demonstrated a strong correlation of the MV2C and MV2K phenotypes with the relative populations of protease-resistant forms of the pathogenic prion proteins, resPrP^D-129 M and resPrP^D-129 V, where resPrP^D-129 M dominated in the sCJDMV2C variant and resPrP^D-129 V in the sCJDMV2K variant. This finding suggests an important, previously unrecognized mechanism for phenotypic determination in human prion diseases.