Different neurotransmitters influence circadian changes and sleep disorders (insomnia, parasomnias, circadian rhythm sleep-wake disorders, hypersomnolence, sleep-related movement disorders, and sleep-related breathing disorders), including melatonin, histamine, GABA, hypocretin, dopamine, noradrenaline, serotonin, and adenosine. This evidence concerns the gene HCRT and sleep disorder.