The reports for the association of other sex hormone candidate gene polymorphisms with endometriosis risk and their functionality in the pathogenesis of endometriosis [45,46,47] show that the genetic background of altered estrogen signaling and production in endometriosis development is a complex genetic trait not restricted to SNVs on the genetic region of ESR1 on 6q.21. Here, ESR1 is linked to endometriosis.