Intriguingly, Bhlhe40, Dbp and Nr1d2 are among the top-ranked genes that are rhythmically expressed in the human brain, and individuals with major depressive disorder appear to have lost the alignment between Bhlhe40 and Per2 expression timetables in six brain regions, e.g. in the amygdala (Li et al. 2013). This evidence concerns the gene PER2 and major depressive disorder.