MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer's disease (AD) is the leading cause of dementia characterized by neuronal loss, and pathological accumulation of neurotoxic β‐amyloid (Aβ) and hyperphosphorylated tau proteins, together with damaging chronic inflammation as indicated by activated microglia, which are the resident immune cells in the central nervous system (CNS) where they are important players in health as well as disease.