HSD17B1 and polycystic ovary syndrome: Patients with polycystic ovary syndrome may have follicle development impairment due to elevated levels of estrogen and pregnenolone in follicular fluid; the mechanism is in part mediated by changes in the expression of HSD17B1, CYP19A1, and CYP11A1 in FF exosomes (Yu et al., 2021).