Abstract: The etiology of polycystic ovary syndrome（PCOS） is not well known so far. Genetics and environment factors can not completely explain its pathogenesis. At present， it has been accepted that epigenetics is involved in the development and inheritance of PCOS. Epigenetic refers to change in gene expression other than in DNA sequence. Epigenetic modification involves DNA methylation， histone modification， X?-chromosone inactivation，genomic imprinting， and so on. DNA methylation status and X chromosome inactivation affect the expression of androgen receptor gene and insulin gene， which could change androgen activity. Histone deacetylase inhibitors increase the accumulation of CYP17 and P450scc mRNA， and further increase androgen level. All of them will eventually lead to PCOS pathogenesis.

Key words: Polycystic ovary syndrome, Genetics, medical, Animals, genetically, Epigenetics, DNA methylation, X chromosone inactivation