BDNF and depressive symptom measurement: We also investigated the correlation between serum sortilin levels and BDNF in addition to the correlation between serum sortilin and vascular endothelial growth factor A (VEGF) levels, another neurotrophic factor suggested to have a role in the pathophysiology of depression.21 A secondary aim of the study was to identify determinants influencing the serum sortilin level and to build a multivariate model.