In univariable meta-regression models, we found a negative relationship between BDNF levels and severity of manic symptoms according to YMRS scores in persons with acute mania, and of depressive symptoms according to HDRS scores in persons with a current depressive episode, indicating that the greater the severity of manic and depressive symptoms, the greater the decrease in BDNF levels (Table 1, Fig. 3b, c). The gene discussed is BDNF; the disease is major depressive disorder.