CHAT and Huntington disease: Perry et al. (1973) reported marked reductions in the levels of GABA in the caudate, globus pallidus, and substantia nigra in HD. Bird and Iversen (1974) confirmed the GABAergic deficits in the caudate-putamen but also revealed cholinergic deficits, reporting significantly reduced activity of choline acetyltransferase (ChAT), the synthetic enzyme for acetylcholine.