Since E2 is important for regulating follicle growth as well as for the selection and atresia of subordinate follicles [26], any alteration in the E2 concentration and/or in the activity of estrogenic signaling mediated by estrogen nuclear receptor ERα and ERβ (with four isoforms in GCs [28]) may lead to PCOS dysfunctions. The gene discussed is ESR2; the disease is polycystic ovary syndrome.