Circadian Genes in Major Depressive Disorder

<b>Background:</b> A core symptom of major depressive disorder (MDD), is sleep disturbance, specifically hypersomnia or insomnia. Sleep is highly regulated by circadian rhythms, controlled by circadian genes, that act through a series of feedback loops to regulate the sleep-wake cycle. <b>Objectives:</b> To the best of our knowledge, a systematic review regarding the core circadian genes and their role in MDD has not been published recently. More specifically, a review of these genes and their role in sleep disturbances in depressed individuals appears to have never been done. As such, we decided to integrate both concepts into one comprehensive review. <b>Method:</b> The review was done using the appropriate search terms in the following search engines: OVID Medline, Embase, PsycINFO and Pubmed. <b>Results:</b> Despite the numerous genetic studies done, few have yielded positive findings. Of those that have, frequently there are other studies that are unable to replicate the original findings. Based on the data summarized in this review, none of the circadian genes appear to be associated with MDD, but a few are more promising than others. These genes are: <i>CRY1</i>, <i>CRY2</i>, <i>PER2</i> and <i>NPAS2</i>. When investigating the role of circadian genes in sleep disturbances among individuals with MDD, the most promising candidate gene is <i>TIMELESS.</i> Although the results in this area are limited further research is warranted. <b>Conclusion:</b> Given the promising leads from this review, future studies should investigate circadian genes in sleep disturbances among the depressed population.