MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer’s disease (AD), the world-leading cause of dementia, is defined by the appearance of two hallmark pathological lesions, amyloid plaques [extracellular aggregates of amyloid-β (Aβ) peptides] and neurofibrillary tangles (intracellular aggregates of hyperphosphorylated tau, or NFTs).