The serum BDNF levels were markedly decreased in patients with depression compared with patients without depression and healthy cases (10.96 ± 2.12 vs. 13.85 ± 2.47, 10.96 ± 2.12 vs. 14.35 ± 2.70, respectively; P ≤ 0.05). The gene discussed is BDNF; the disease is major depressive disorder.