ESR2 and endometriosis: Although the involvement of the ER subtypes (ERα and ERβ) in the progression of endometriosis is not clear [67, 68], the results obtained from the present study of North Indian women concur with the findings reported by Zhang et al. (2018), who also did not observe any change in the levels of the wild type ERα mRNA in a population of fertile Chinese women with and without endometriosis [69].