In PCOS patients, this nuclear receptor activation is probably due to the local hyperoestrogenic uterine environment in infertile ovulatory PCOS patients and the unopposed oestrogen environment in anovulatory PCOS endometria where oestrogen levels are modulated by hydroxysteroid dehydrogenase (HSD) enzymes [38]. This evidence concerns the gene CHST3 and polycystic ovary syndrome.