The causes of AD are poorly understood, although several etiological factors, such as genetic abnormalities, history of head injuries, environmental factors, general lifestyles, depression or hypertension, deposition of extracellular ß-amyloid protein (Aβ) and microtubule associated tau protein in the brain, and cholinergic dysfunction have all been implicated in AD. Here, MAPT is linked to Alzheimer disease.