Regarding other treatments less used in BD, such as recombinant erythropoietin (EPO), one study explored the effect of EPO on peripheral BDNF levels in patients with affective disorders, and found that it decreased plasma BDNF levels in patients with treatment-resistant depression, but no effect on these levels was observed in patients with BD treated with EPO [50]. The gene discussed is BDNF; the disease is depressive symptom measurement.