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), which alter steroid signaling and responsiveness, and are critically involved in development and decidualization [3], [4],[22]–[24]. The gene discussed is HOXA10; the disease is endometriosis.