BTD and major depressive disorder: One such study revealed 161 dysregulated proteins in 40 MDD patients,15 of which 12 were associated with depressive symptoms in our study in both cohorts: APP, ATPase H+ transporting accessory protein 1 (ATP6AP1), biotinase (BTD), calsyntenin‐1 (CLSTN1), CST3, MAG, neurofascin (NFASC), opioid‐binding protein/cell adhesion molecule (OPCML), RELN, testican‐1 (SPOCK1), transmembrane protein 59 like (TMEM59L), and WAP four‐disulfide core domain 2 (WFDC2).