GREB1 and endometriosis: Nevertheless, the association was not considerable when only stages III and IV and, thus, more aggressive of endometriosis, were considered, which suggests relation of the polymorphism with the initial stages of the disease.15 Another study assessing the relation between GREB1 with endometriosis verified the relevance of rs13394619, although various other polymorphisms in the same gene had superior significance, suggesting greater relevance in the development and severity of endometriosis.17