Peripheral BDNF levels were equally decreased in mania and depression (P = 0.340, 34 comparisons, n = 2,471), and both manic and depressive states presented BDNF levels to be decreased when compared to the euthymic state (P = 0.014, 43 comparisons, n = 4,454 for mania vs. euthymia; P = 0.001, 39 comparisons, n = 4,131 for depression vs. euthymia; Bonferroni correction for multiple comparisons applied). The gene discussed is BDNF; the disease is major depressive disorder.