AD, the most frequent neurodegenerative aetiology of neurocognitive disorders, is marked pathologically by plaques composed of ß amyloid deposits (Aß) surrounded by dystrophic neuritis, neurofibrillary tangles composed of hyperphosphorylated tau, with activated microglia and reactive astrocytes, neuronal and synaptic loss. The gene discussed is MAPT; the disease is Alzheimer disease.