MAPT and early-onset autosomal dominant Alzheimer disease: Accumulation of hyperphosphorylated microtubule-associated tau protein (MAPT, tau) in neurons and glia is a hallmark of a wide range of neurodegenerative diseases.1 Disorders associated with the accumulation of MAPT are thus termed tauopathies, which include Alzheimer’s disease (AD) as well as progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Pick’s disease (PiD) among the non-AD tauopathies.