Experimental and clinical studies have clearly demonstrated that the cholinergic hypofunction and/or denervation due to imbalance in NGF/TrkA signaling pathway are causally related to MCI at prodromal stages of AD neuropathology (Mufson et al., 2000, 2002, 2008; Salehi et al., 2003; Niewiadomska et al., 2011; Schliebs and Arendt, 2011; Hampel et al., 2018). The gene discussed is NTRK1; the disease is Alzheimer disease.