In AD, the cholinergic system is affected due to various processes including the following: (1) Altered NGF maturation, (2) Skewed TrkA/p75 receptor ratio, (3) Inefficient axonal transport and signaling, (4) Aβ induced modulation of NGF receptors, (5) Suboptimal ACh innervation induced inflammatory response, and (6) Aβ cytotoxicity. This evidence concerns the gene NTRK1 and Alzheimer disease.