CHAT and Cognitive impairment: Over the past several years, researchers have revealed that choline acetyltransferase (ChAT) activity decreased and acetylcholinesterase (acetylcholinesterase, AchE) activity increased in patients with AD, which led to a decrease in acetylcholine (Ach) level and occurrence of dementia symptoms mainly characterized by learning and memory impairment and cognitive impairment [117].