MAPT and early-onset autosomal dominant Alzheimer disease: The advent of tau-specific ligands for use with positron emission tomography (PET), however, has now made it possible to investigate tau deposition at early stages of several neurodegenerative disorders, including Alzheimer’s disease (AD), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and related conditions such as Down’s syndrome (DS), Parkinson’s disease (PD), and dementia with Lewy bodies (DLB).