The pathogenesis of endometriosis has also been associated with excessive production of estrogens by up-regulated expression of aromatase and 17β-HSD type 1, and suppression of 17β-HSD types 2 and 4, collectively resulting in an increased ratio of estradiol-17β to estrone in ectopic tissues[39-42]. The gene discussed is CYP19A1; the disease is endometriosis.