MTNR1B (Melatonin Receptor 1B): MTNR1B is a gene that encodes one of the receptors for melatonin, a hormone responsible for regulating sleep and circadian rhythms. This receptor plays a key role in maintaining the body’s internal clock and is also involved in glucose regulation. Variations in MTNR1B have been associated with an increased risk of type 2 diabetes and disrupted sleep patterns.