MAPT and early-onset autosomal dominant Alzheimer disease: Primary tauopathies such as corticobasal degeneration (CBD) and Pick’s disease (PiD) exhibit only tau inclusions, whereas Alzheimer’s disease (AD), a secondary tauopathy, is characterized by the presence of extracellular beta-amyloid (Aβ) plaques and intracellular neurofibrillary tau tangles 1–4.