In the literature, the main genes involved in the epigenetic pathway of endometriosis pathogenesis [7,8,9,14] seem to be the estrogen and progesterone receptors ERα (hyper-methylation), Erβ (hypo-methylation) and Prβ (hyper-methylation) [21], the aromatase (development of hyperestrogenic microenvironment) [22], the homebox protein HOXA-10 (hyper-methylation with reduced uterine receptivity), and the Cyclooxygenase COX-2 (over-production of PGE2) [23]. The gene discussed is PGR; the disease is endometriosis.