SERPINI1 and major depressive disorder: In line with the results of the combined MRM cohort, the independent analysis of these two cohorts revealed four proteins (CNTNAP4, SERPINI1, NRXN3, and GRIA4) that were significantly downregulated in the CSF of MDD patients in both cohorts (iTRAQ-MDD vs iTRAQ-Con, p < 0.05 and new-MDD vs new-Con, p < 0.05).