Depression may be associated with a cognitive impairment through a variety of mechanisms, including loss of hippocampal volume caused by excessive secretion of corticosteroids, resulting in neurotoxicity; inhibition of hippocampal neurogenesis [42,43]; increased deposition of b-amyloid plaques; and lack of nerve growth factors such as brain-derived neurotrophic factor affect cognitive function [44]. The gene discussed is BDNF; the disease is major depressive disorder.