NTRK1 and hereditary spastic paraplegia: NGF and its receptors (e.g., TrkA, TrkB, p75NTR) are found in a wide range of neurons including those within cortical regions of the brain affected in HSP such as the hippocampus, somatosensory and motor cortex, as well as those implicated in complicated forms such as the cerebellum (Pitts and Miller, 1995; Conner et al., 2009).