BDNF and major depressive disorder: However, we found a large overlap in patients with MDD and controls (mean levels and standard deviations were 20,321.2 ± 8180.0 pg/ml in MDD patients and 27,105.5 ± 8310.2 pg/ml in controls), and there were patients with MDD whose serum BDNF levels were not lower than the control mean.