Estrogen signal medicated by estrogen receptor (ER), which is involved in various diseases related to steroid hormone, such as cancer. A number of association studies have focused on ESR2 polymorphisms to investigate the relationship with cancer risk. The development of endometriosis is associated with changes in the expression of genes encoding the 3beta-hydroxysteroid dehydrogenase type II (HSD3B2) and 17beta-hydroxysteroid dehydrogenase type II (HSD17B2), estrogen receptors 1 (ESR1) and 2 (ESR2) and the androgen receptor (AR). Estrogen receptor 2 (ESR2) plays a critical role in folliculogenesis and ovulation. Disruption of ESR2-function in the rats results in female infertility due to failure of ovulation, that ESR2 regulates key genes in GCs that are essential for follicle maturation and ovulation in the rat. There is a strong association between ESR2 SNPs and BMD, indicating that ESR2 may influence attainment of bone mass.