CHAT and Alzheimer disease: Over the past decades, it has been proposed that as AD advances, the degeneration of the cholinergic system is characterized by a decrease in acetylcholine (Ach), ChAT, and an enhancement of acetylcholine esterase (AchE) in the basal forebrain, cortex, and hippocampus which is known as the cholinergic hypothesis [9, 10].