CHRNA4 and Parkinson disease: Considering the significant loss of nAChRs in PD brain with α-synuclein over expression, the neurotoxicity of α-synuclein to SNc dopaminergic neurons, the extensive distribution of cholinergic innervations and their receptors in SNc dopaminergic neurons, and the neuroprotective effects provided by nAChR activation [27], [28], [29], it is reasonable to hypothesize that α-synuclein might perturb cholinergic signaling by impairing nAChRs function.