INS and major depressive disorder: Consistent with the present study, insulin was found to be increased in MDD in one proteomic study,13 but not in our previous proteomic analysis including all MDD cases in the cohort.11 Our finding that leptin was increased in atypical depression is consistent with a previous study in atypical depression39 and more recently was confirmed in the NESDA sample that also confirmed the absence of an association with melancholic depression.40 It implies leptin resistance—which is thought to contribute to depressive symptomatology41—as an underlying mechanism in atypical depression.