MAPT and Alzheimer disease: In this perspective, we will start by discussing the situation in AD, which is associated with the extracellular precipitation of amyloid β peptide, Aβ, and intracellular precipitation of the protein tau (Scheltens et al., 2016; Bondi et al., 2017; Lane et al., 2018; Walsh and Selkoe, 2020; Scheltens et al., 2021).