PTCH2 and major depressive disorder: Among the identified DEGs, nine genes were repeatedly identified, i.e., identified in two comparisons: HSPH1 and IGKC in comparisons between MDD patients and controls and between responders and nonresponders to SSRIs; BTNL8, KATNBL1, LYVE1, MIR15A, PTCH2, and SCARNA17 in comparisons between MDD patients and controls and between baseline and 6 weeks after SSRI treatment; and FCRL6 in comparisons between responders and nonresponders to SSRIs and between baseline and 6 weeks after SSRI treatment (Table 3).