MAPT and early-onset autosomal dominant Alzheimer disease: Sporadic Alzheimer's disease (AD) is a progressive chronic neurodegenerative disorder (at least 97% of all cases are non-genetic) and is characterized by severe beta-amyloid (Aβ) deposition in brain (plaques) and in vessels (cerebral Aβ angiopathy, CAA), Tau pathology, cell death of cholinergic neurons, microglial activation, inflammation and cerebrovascular damage.