Under the assumption that these two disorders share common pathophysiologic mechanisms involving protein aggregation in the brain leading to fatal degeneration, we investigated a possible genetic interaction between APOE ε4 allele and the polymorphic codon 129 of the PRNP gene in both AD and CJD populations compared to a common control population (Calero et al., 2011). This evidence concerns the gene APOE and Creutzfeldt Jacob disease.