AD is the most common cause of dementia in elderly. Pathogenesis remains unclear, but involves accumulation of neurotoxic proteins, amyloid beta (Aβ-amyloid) and tau, with decrease in ACh neurotransmission by cholinergic neurons in the nucleus basalis of Meynert. AD can occur with no reason, or it can be genetic (can involve presenilin mutations: presenilin-1 "chromosome14" and presenilin-2 "chromosome1"). The disease can be mild, moderate, or severe. Treatment is by acetylcholinesterase inhibitors or NMDA receptor antagonist.