MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer’s disease (AD) is a secondary tauopathy, in which amyloid plaques feature as an additional histopathological feature, a characteristic that is lacking in primary tauopathies such as frontotemporal lobar degeneration with tau (FTLD-tau), argyrophilic grain disease, progressive supranuclear palsy, or corticobasal degeneration (Polanco et al, 2018b; Chung et al, 2021).