MAPT and early-onset autosomal dominant Alzheimer disease: [18F]AV‐1451 was developed as a specific marker of paired helical filament tau (PHF‐tau) pathology in Alzheimer's disease (AD), and is selective for PHF‐tau over beta‐amyloid and alpha‐synuclein in vitro.1 In vivo studies have confirmed elevated and distributed binding in keeping with typical and atypical presentations of Alzheimer's disease,2, 3 consistent with Braak staging.4 Binding characteristics in neurodegenerative diseases other than Alzheimer's disease are controversial.