PTP4A2 and major depressive disorder: Furthermore, the most significant proteins for suicide in the WGCNA analysis included CAPNS1 (Calpain Small Subunit 1), which is suggested to play a neuroprotective role [54], and CSNK2B and PTP4A2, implicated as biomarkers for psychiatric disorders such as major depressive disorder and schizophrenia [55–57].