The levels of total tau protein, 14-3-3 protein, and protease-resistant isoform of prion protein (PrP<sup>res</sup>) in the cerebrospinal fluid; periodic sharp wave complexes on electroencephalography; and diffusion-weighted imaging (DWI) of brain magnetic resonance imaging (MRI) have all been used to diagnose symptomatic CJD, but none of these markers have been established in the diagnosis of presymptomatic CJD. This evidence concerns the gene PRNP and Creutzfeldt Jacob disease.