CHAT and early-onset autosomal dominant Alzheimer disease: Interest in the forebrain cholinergic system has been greatly stimulated by the observation that postmortem Alzheimer's disease brains exhibit a decrease in the number of cell bodies of cholinergic neurons in the basal forebrain and a parallel loss of enzymes involved in cholinergic transmission (e.g. ChAT) in the cerebral cortex [38]–[41].