Whether small but statistically significant differences in methylation levels could affect gene expression levels is currently unknown, but previous studies have shown that the members of HOXA cluster, HOXA10 and HOXA11 were differentially methylated in stromal cells obtained from endometriomas [14] and in eutopic endometria from patients [6, 7, 9, 29, 30] compared to healthy controls, and hypermethylation of the HOXA genes was accompanied by lower transcript and protein levels in endometrium of endometriosis patients [6, 9]. Here, HOXA11 is linked to endometriosis.