NTRK1 and hereditary spastic paraplegia: However, as TrkA is expressed extensively in the cholinergic system of the basal forebrain that contain extensions that innervate various regions that affect cognition, learning, and motor control, there may be a role of KIF1A-mediated TrkA trafficking dysfunction in some complicated forms of HSP (Sobreviela et al., 1994; Wu et al., 2014).