Abnormal DNA methylation in endometriosis affects the expression of several genes, including homeobox A10 (HOXA10), estrogen receptor beta (ESR2), steroidogenic factor 1 (NR5A1), and aromatase (CYP19A1); these, in turn, alter steroid signaling and responsiveness and are critically involved in development and decidualization. This evidence concerns the gene ESR2 and endometriosis.