ESR1 and polycystic ovary syndrome: In polycystic ovarian syndrome (PCOS), where epigenomic instability affects Fshr, Cyp19a1, Esr1, and Igf1, PFASs intensify transcriptional repression through DNMT3A-mediated CpG hypermethylation and global hypoacetylation of H3K9 and H4K16 [101].