Previously, our laboratory has shown that STRA6 is the principal regulator of retinol uptake in the endometrium and that the decreased expression of this gene in endometriosis can contribute to decreased hydroxysteroid (17-beta) dehydrogenase 2 (HSD17β2) mRNA expression [13], leading to persistently elevated levels of estradiol. This evidence concerns the gene HSD17B2 and endometriosis.