Altered expression of circadian rhythm genes among individuals with a history of depression.

BACKGROUND: Depression has been associated with several circadian rhythm perturbations, suggesting a disruption of the circadian clock system in affective disorders. The interaction of several circadian clock genes generates these daily circadian rhythms. METHODS: This cross-sectional study evaluated whether circadian gene expression differed between individuals with a history of depression and participants without a similar history. The participants were 60 healthy older adults. Half of the participants had a history of depression. Real-time quantitative polymerase chain reaction was used to measure the circadian gene Clock, BMAL1, Period1, and Period2 messenger RNA levels in peripheral blood leukocytes. RESULTS: Individuals with a history of depression had higher Clock, Period1, and Bmal1 mRNA levels, compared to non-depressed participants. LIMITATIONS: Although circadian gene expression fluctuates throughout the day, clock gene mRNA levels were evaluated only in the morning. CONCLUSIONS: These results suggest that disruptions of the molecular mechanisms underlying the circadian clock system may be associated with depression.