CHAT and Rett syndrome: Postmortem immunohistochemical studies of the brain from individuals with Rett Syndrome have shown profound cholinergic deficits: there are reduced numbers of choline acetyltransferase (ChAT)-positive cells in the basal forebrain, reduced ChAT and VAChT activity, and reduced cholinergic receptor expression (Kitt et al., 1990; Wenk and Mobley, 1996; Wenk, 1997; Wenk and Hauss-Wegrzyniak, 1999; Yasui et al., 2011).