MAPT and Alzheimer disease: The microtube-binding domain, enclosedeither by three (3R) or four (4R) repeating subdomains, is foldedto be β-sheet rich and is aggregated chain by chain in the formationof the tau fibrils.5,6 Components of such tau fibrilsvary for different tauopathies, and while both 3R tau and 4R tau arepresent in AD and CTE, only 4R tau is found in CBD, GGT, AGD, andPSP, and 3R in PiD.