CHAT (choline acetyltransferase, CAT, CHOACTASE) is an enzyme that catalyzes the biosynthesis of the neurotransmitter acetylcholine. CHAT has important functions in the cholinergic system and is expressed by (and may be used to identify) cholinergic neurons, whose neurodegeneration is a typical component of Alzheimer’s disease. CHAT variants and change-of-function mutations are correlated with Alzheimer's disease, mild cognitive impairment, and congenital myasthenic syndrome with episodic apnea. In immunohistochemistry, CHAT has cytoplasmic positivity in cholinergic nerve endings in the brain, and is also found in specific cell populations in the gastrointestinal tract and in placental stroma. References: Curr Neuropharmacol. 2016 Jan; 14(1): 101–115, PMID: 26813123; Dement Geriatr Cogn Disord. 2008;26(1):9-14, PMID: 18562794; J Neuropathol Exp Neurol. 57 (1): 63–75, PMID: 9600198;