HSPG2 and polycystic ovary syndrome: Although requiring further investigations, this hypothesis is strengthened by the decline in the concentration of E2-binding and E2-protecting proteins such as sex-hormone-binding globulin (SHBG), albumin and heparan sulfate proteoglycan 2/perlecan (another proposed estrogen-binding protein in the FF [45]) in PCOS FF [42,46,47].