In this article, it discusses the role of misplaced stem cells in the formation of endometriosis, indicating the genetic involvement. Misplaced stem cells (outside the uterus) are activated in women with endometriosis and the cells will respond to hormonal changes the same way that the lining of the uterus does. This, in turn, initiates an immune response (macrophages) which releases several chemicals that can cause pain and inflammation.
"Conclusion:
Dysregulation of Wnt and/or Hox genes may affect cell migration during organogenesis and differentiation of Müllerian structures of the female reproductive tract, with possible dislocation and dissemination of primordial endometrial stem cells in ectopic regions, which have high plasticity to differentiation. We hypothesize that during postpubertal age, under the influence of different stimuli, these misplaced and quiescent endometriotic cells could acquire new phenotype, biological functions, and immunogenicity. So, these kinds of cells may differentiate, specializing in epithelium, glands, and stroma to form a functional ectopic endometrial tissue. This may provoke a breakdown in the peritoneal cavity homeostasis, with the consequent processes of immune alteration documented by peripheral mononuclear cells recruitment and secretion of inflammatory cytokines in early phases and of angiogenic and fibrogenic cytokines in the late stages of the disease."
http://www.hindawi.com/journals/ogi/2013/527041/