SFRP4 and polycystic ovary syndrome: Many genes related with oocyte meiosis and maturation were differentially expressed in PCOS oocytes compared with non-PCOS oocytes, including epidermal growth factor receptor (EGFR), progesterone receptor (PGR), progesterone receptor membrane component 1 (PGRMC1), phospholipase C, zeta 1 (PLCZ1), secreted frizzled-related protein 4 (SFRP4), and zinc finger, MIZ-type containing 1 (ZMIZ1) and zinc finger and SCAN domain containing 4 (ZSCAN4) (Fig. 5A).