Alzheimer's disease is a progressive brain disorder that causes memory loss and cognitive decline. It was first described by Alois Alzheimer in 1906 from examining brain tissue of a deceased patient. The causes are unknown but risk factors include age, family history, and head injuries. Pathologically, it involves the buildup of beta-amyloid plaques and tau protein tangles in the brain which destroy connections between neurons. There is no cure and the prognosis is a gradual worsening of symptoms ultimately leading to death, on average within 7-10 years of diagnosis.