PER3 and major depressive disorder: Interestingly, rs228697 of hPer3 is significantly associated with altered phasing of daily activity/sleep timing,48 which together with our observations (Tables 1 and 2, Supplementary Table S5 and Figure 2) resurrects a hypothesis that MDD is at least partially due to suboptimal phasing of activity/sleep with the environment.2, 3, 4, 6 If true, circadian phase resetting may be an effective therapy.