MAPT and Alzheimer disease: Recent studies suggest that there may be changes in cell cycle reentry of hippocampal and cortical neurons in AD that may precede the observed proteinopathies (i.e., beta-amyloid fibrils and tau tangles) in AD (Arendt et al., 1996; Frade and Ovejero-Benito, 2015; Nativio et al., 2018; Beckmann et al., 2021; Portillo et al., 2021).