BDNF and bipolar disorder: As a result of these neuroplastic qualities BDNF levels have been explored in patients with bipolar disorder, and based on reviews and meta-analyses BDNF is suggested as a potential biomarker related to neuroprogression and disease activity.9,10 Two recent meta-analyses including 53 studies11 and 52 studies,10 found that patients with bipolar disorder tend to have lower peripheral BDNF levels during both depressive and manic episodes compared with healthy controls, and that BDNF levels may return to normal in euthymic states.