Serum and plasma BDNF levels are lower in patients with depression than in healthy controls, indicating a negative correlation between the severity of the depression and serum BDNF (Bus et al., 2015; Lee et al., 2007; Molendijk et al., 2011, 2014; Yoshimura et al., 2007). The gene discussed is BDNF; the disease is depressive symptom measurement.