Polymorphisms in circadian genes (CLOCK gene, PER3, peroxisome proliferator-activated receptor-c coactivator-1a) [30,31,32,33] and neuromodulators involved in the sleep-wake regulation have been associated with insomnia, sometimes in association with depressive symptoms, especially when serotoninergic pathways were involved [34,35,36,37]. This evidence concerns the gene CLOCK and insomnia.