Thus, we conclude that dysregulated 17β-HSD1 expression and alterations in the PRA:PRB ratio resulting in hyperestrogenism and progesterone resistance during the secretory phase of the menstrual cycle, rather than an anomaly in aromatase expression, were the hallmarks of the eutopic endometrium of infertile patients with OE. The gene discussed is CYP19A1; the disease is hyperestrogenism.