ABSTRACTIn 2007, we reported a patient with an atypical form of Creutzfeldt-Jakob disease (CJD) heterozygous for methionine-valine (MV) at codon 129 who showed a novel pathological prion protein (PrP^TSE) conformation with an atypical glycoform (AG) profile and intraneuronal PrP deposition. In the present study, we further characterize the conformational properties of this pathological prion protein (PrP^TSEMV^AG), showing that PrP^TSEMV^AGis composed of multiple conformers with biochemical properties distinct from those of PrP^TSEtype 1 and type 2 of MV sporadic CJD (sCJD). Experimental transmission of CJD-MV^AGto bank voles and gene-targeted transgenic mice carrying the human prion protein gene (TgHu mice) showed unique transmission rates, survival times, neuropathological changes, PrP^TSEdeposition patterns, and PrP^TSEglycotypes that are distinct from those of sCJD-MV1 and sCJD-MV2. These biochemical and experimental data suggest the presence of a novel prion strain in CJD-MV^AG.IMPORTANCESporadic Creutzfeldt-Jakob disease is caused by the misfolding of the cellular prion protein, which assumes two different major conformations (type 1 and type 2) and, together with the methionine/valine polymorphic codon 129 of the prion protein gene, contribute to the occurrence of distinct clinical-pathological phenotypes. Inoculation in laboratory rodents of brain tissues from the six possible combinations of pathological prion protein types with codon 129 genotypes results in the identification of 3 or 4 strains of prions. We report on the identification of a novel strain of Creutzfeldt-Jakob disease isolated from a patient who carried an abnormally glycosylated pathological prion protein. This novel strain has unique biochemical characteristics, does not transmit to humanized transgenic mice, and shows exclusive transmission properties in bank voles. The identification of a novel human prion strain improves our understanding of the pathogenesis of the disease and of possible mechanisms of prion transmission.