PRNP and Alzheimer disease: For the fibrils shown in Fig. 12, the volume of EDs compared to the volume of protein density is 13.5% for a22L mouse scrapie (PrP fibril, single protofilament, EMDB 28089, PDB 8efu7), 8.5% for GSS (PrP fibril, paired protofilaments, EMDB 26613, PDB 7un528), 9.0% for AD (tau PHF fibril, paired protofilaments, EMDB 26663, PDB 7upe34) and 4.3% for MSA (alpha-synuclein fibril, paired protofilaments, EMDB 10650, PDB 6xyo17).