Although BDNF has been demonstrated to hold potential in altering AD pathology and counter cognitive decline through its roles in the neurogenic niche and the function of NSCs, its inability to cross the blood–brain barrier (BBB), its poor pharmacokinetic properties and its vulnerability to proteolytic cleavage remain important limitations in using BDNF as a reliable therapeutic agent. The gene discussed is BDNF; the disease is Alzheimer disease.