NTRK1 and osteoporosis: In addition to roles in development and maintenance of sensory and sympathetic neurons,19 NGF plays a role in bone differentiation27 and bone fracture repair.11 Most sensory nerve fibers in bone express the high-affinity NGF receptor TrkA.8,12,26,36 In osteoporosis, proinflammatory cytokines, such as TNFα and IL-1β, increase in bone marrow; NGF regulates these substances.20 The efficacy of anti-NGF therapy in musculoskeletal-related pain may be mediated, in part, by a reduction in NGF-maintained inflammation.