OPRK1 and depressive disorder: DUSP6 overexpression also increased mRNA levels for the kappa opioid G-protein coupled receptor, which has been implicated in memory and depression (Bilkei-Gorzo et al., 2012; Bodnar, 2023; Wang et al., 2023; Zhu et al., 2024), and additionally, OPRK1 promoter methylation that leads to reduced gene expression has been found to increase AD risk (Ji et al., 2015).