SLC6A4 and major depressive disorder: Similarly, in a larger study involving 349 volunteers, depressed volunteers displayed higher levels of NR3C1 DNA methylation and lower cortisol levels (Borçoi et al., 2020), providing evidence for the role of glucocorticoid level changes, NR3C1, and SLC6A4 DNA methylation in HPA axis dysregulation in depression patients, warranting further exploration.