MAPT and Alzheimer disease: For example, a cryo-EM study performed at 3.4–3.5 Å resolution has demonstrated that the filament core of tau filaments isolated from human AD brains is comprised of residues 306–378, which adopt a crosslinked β-sheet structure and form the seed for tau aggregation, whereas the PHFs and straight filaments (SFs) differ in their intermolecular protofilament packing.