Our observed decrease of Arntl expression in the hippocampus of subjects with MDD is in line with reports of weaker molecular clock rhythms in subjects with MDD (Li et al., 2013), and rodent studies suggest weaker rhythms in depression may result from decreased Arntl expression in the suprachiasmatic nucleus (Landgraf et al., 2016; Vadnie et al., 2021). Here, CLOCK is linked to major depressive disorder.