MAPT and early-onset autosomal dominant Alzheimer disease: Accumulation of the abnormally phosphorylated and aggregated microtubule associated protein tau (MAPT, or tau) is a main hallmark of Alzheimer's disease (AD) and other tauopathies1–3, including frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP17), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), Pick’s disease (PiD), and chronic traumatic encephalopathy.