PCSK9 and major depressive disorder: There was no association between reduced PCSK9 protein levels and MDD (stringent-PSMR-multi = 0.209, relaxed-PSMR-multi = 0.253), mood instability (relaxed-PSMR-multi = 0.019, stringent-PSMR-multi = 0.012), or neuroticism score (relaxed-PSMR-multi = 0.047, stringent-PSMR-multi = 0.039) (Fig 1, Table 1, data in S2 and S4 Tables).