Candidate gene studies have associated PCOS with several genes, including the insulin receptor gene (INSR) [25], insulin-like growth factor (IGF) system genes, luteinizing hormone (LH) /chorionic gonadotropin receptor gene (LHCGR) [26], genes involved in androgen biosynthesis and steroid hormone metabolism (CYP11) [25], and the melatonin receptor genes (MTNR1A and MTNR1B) [27]. Here, MTNR1B is linked to polycystic ovary syndrome.