In these diseases, while the disease-causing amyloidogenic proteins (β-amyloid protein (AβP) in AD, prion protein (PrP) in prion disease, and α-synuclein in Lewy body disease) differ substantially in primary sequence, they have the common ability to form cytotoxic amyloid fibrils composed of oligomers with β-pleated sheets. This evidence concerns the gene PRNP and prion disease.