There was no difference in serum BDNF levels between the two subgroups of MDD patients stratified according to illness severity (mild, n = 35, vs moderate and severe, n = 16), history of suicide attempts (no, no = 33, vs yes, n = 18), and LDAEP values (dichotomized at the median into low, n = 26, vs high, n = 25; Table 1). Here, BDNF is linked to major depressive disorder.