Previous studies showed that type 2 diabetes significantly affects myocardial infarction risk, and that MTNR1B gene polymorphisms are associated with increased diabetes risk, that the same receptor has a stronger protective effect against myocardial ischemia, and that MTNR1B gene polymorphisms are associated with circadian phenotype—chronotype. The gene discussed is MTNR1B; the disease is myocardial ischemia.