PET imaging studies with tracers for both pre- and post-synaptic cholinergic targets have confirmed the abnormalities of cholinergic transmission in vivo, in AD, as manifested in altered levels of AChE, VAChT, and α4β2 and α7 nAChR's, and their correlations with Aβ deposition and cognitive functions. This evidence concerns the gene CHRNA7 and Alzheimer disease.