OXT and major depressive disorder: In conclusion, we found in our longitudinal study the following: (a) plasma oxytocin to be unrelated with depression, (b) lower urinary oxytocin levels in depressed patients, (c) lower exon 1 OXTR DNA methylation in depressed patients, and (d) plasma, urinary oxytocin, and OXTR-related factors to be statistically unrelated with each other.