Alzheimer’s disease (AD), which is characterized by the deposition of β-amyloid peptide (Aβ) in senile plaques, neurofibrillary tangles composed of hyperphosphorylated tau, loss of specific subsets of neurons, and neuroinflammation resulting from astrogliosis and microglial activation, is the main cause of dementia. The gene discussed is MAPT; the disease is Alzheimer disease.