MAPT and Alzheimer disease: Alzheimer’s disease and CBD filaments eventually appear in the patient’s brain as PHF/SF or type I (singlet)/type II (doublet), respectively.34,36,44 However, tau filaments seeded with Alzheimer’s disease and CBD filaments in this cellular model were identified only as protofilaments, suggesting that the interaction of two protofilaments requires some intracellular event(s), such as the N- and C-terminal truncation of tau.