Nerve growth factor (NGF) is the first identified neurotrophic factor that has the biological function of nourishing neurons and promoting protrusion growth, and has an important role in the development, differentiation, growth, and regeneration of central and peripheral neurons, and is widely expressed not only by neurons and glial cells, but also detected in peripheral cells, and reduces neuronal death in AD via the NGF/TrkA/PI3K pathway. The gene discussed is NGF; the disease is Alzheimer disease.