Estrogen resistance induced by inactivating mutations in the E2 receptor alpha (ESR1 gene) (Table 2) is a very rare condition that was first described in males; in females, the morphology of external genitalia at birth has not yet been described in detail, but patients develop postnatal virilization by the development of a polycystic ovary with increased levels of androstenedione and T, as well as tall stature and osteoporosis [62]. This evidence concerns the gene ESR1 and osteoporosis.