The brain-derived neurotrophic factor (BDNF), a neurotrophin expressed in the hippocampus, plays an important role in neuronal survival, sinaptic integrity, and neuroplasticity.41 Decreased BDNF levels have been systematically associated with cognitve impairment42,43 and dementia.44-46 Elderly patients with depressive disorders also demonstrated decreased BDNF levels.47,48. This evidence concerns the gene BDNF and depressive disorder.