The involvement of insulin resistance and secondary hyperinsulinemia in the PCOS pathogenesis is complex, implying the existence of many mechanisms.In vivo and in vitro studies have proved that insulin directly stimulates ovarian streroidogenesis at the level of theca cells, along with LH.This co–gonadotropic effect contributes to the PCOS hyperandrogenism. This evidence concerns the gene PLOD1 and polycystic ovary syndrome.