MAPT and Alzheimer disease: Alzheimer disease is the most common cause of dementia, affecting an estimated 6.9 million Americans older than 65 years of age.1 The disease is characterized pathologically by accumulation of amyloid-β (Aβ) plaques and intraneuronal neurofibrillary tangles composed of hyperphosphorylated tau protein (p-Tau).2 Amyloid-β peptides are formed from cleavage of the transmembrane amyloid precursor protein.