MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer’s disease is the major cause of dementia and the seventh leading cause of death in the USA, with prevalence increasing as the population ages.1,3-6 The defining hallmark features of Alzheimer’s disease are β-amyloid (Aβ) plaques and tau neurofibrillary tangles (NFTs).1,3 Previously only detectable post-mortem, positron emission tomography (PET) biomarkers1,7,8 now permit a pathological diagnosis before death.