As observed with the +10 (T/C) and +25 (G/C) polymorphism of the TGF-ß1 gene, other genetic variations of neurotrophic factors, such as the brain-derived neurotrophic factor (BDNF) Val66Met functional polymorphism, increase the risk to develop depression in AD patients [25] and also determine a higher risk of disease-progression in patients with MCI [96]. The gene discussed is BDNF; the disease is major depressive disorder.