Romosozumab/Denosumab Study for Premenopausal IOP

Inclusion Criteria: * Premenopausal women, aged 18-48, with regular menses and no historical or biochemical secondary cause of osteoporosis; the lower age limit is to ensure epiphyses are fused, the upper to make it less likely that women will enter menopause during the study. All subjects under age 25 will be screened (bone age radiograph) prior to enrollment to rule out open epiphyses. * Documented adult fractures judged to be low-trauma (equivalent to a fall from a standing height or less) and T-score or Z-score ≤ -1.5 at the LS, TH or FN. * Must agree to use highly effective contraception throughout the period of study drug administration. Highly effective contraception includes methods considered by the CDC to be \>99% effective (e.g. vasectomized partner, tubal ligation, hysterectomy, IUD) as well as a combination of barrier method (condoms) with hormonal contraception considered to be \> 90% effective (oral contraceptive pill, patch or ring). Systemic progestin only methods (oral or implanted) are not included due to their effect on systemic estrogen levels and thus potential effects on bone health in this premenopausal population. Exclusion Criteria: * Any cardiovascular disease: history of myocardial infarction (MI) or stroke. Normal electrocardiogram (ECG) or ECG with no clinically significant abnormality is required at study entry. * Conditions requiring chronic anticoagulation (coumadin, heparins) * Early follicular phase serum FSH\>20 mIU/ml (to exclude …