Romosozumab is an anti-sclerostin antibody that provides powerful skeletal benefits through concomitant osteoanabolic and antiresorptive effects on bone. In postmenopausal women, romosozumab is associated with larger increases in spine and hip BMD in comparison to teriparatide. Romosozumab has an extremely low reported nonresponse rate and transition to denosumab after romosozumab leads to further BMD increases and sustained anti-fracture efficacy.~Therefore, the investigators hypothesize that romosozumab will be associated with improvements in bone mass in premenopausal women, and also that the responses and response rates will exceed those observed in premenopausal women treated with teriparatide. The investigators will test this hypothesis in this phase 2 study of 30 premenopausal women with IOP who will receive 12M of romosozumab 210 mg monthly followed by 12M of denosumab 60 mg SC q6M (romosozumab-denosumab).~Aim 1 will define the within-group effect of romosozumab-denosumab. The primary outcome variable will be the within-group change in areal BMD by DXA at the lumbar spine at 12M. Secondary outcome variables include change in aBMD by DXA at the total hip, femoral neck and 1/3 radius at 12M and change in aBMD at all sites at 24 months.~Aim 2 will compare results from participants treated with romosozumab-denosumab to the well-characterized historical controls treated with 24 months of teriparatide alone, and a subset of those treated with 24 months of teriparatide followed by 12 months of denosumab. The investigators hypothesize that romosozumab over 12M and romosozumab-denosumab over 24M will be associated with larger BMD gains compared to 12M and 24M of teriparatide. The investigators also hypothesize that 24M of romosozumab-denosumab will be associated with comparable BMD gains vs. historical controls treated with 36M of teriparatide-denosumab.
The overarching goal of the research program is to define optimal treatment for premenopausal women with clinically significant fracture syndromes that require medical therapy. The investigators hypothesize that romosozumab will be associated with improvements in bone mass and microarchitecture in premenopausal women, and also that the responses and response rates will exceed those observed in premenopausal women treated with teriparatide. The investigators will test this hypothesis in this phase 2 study of 30 premenopausal women with idiopathic osteoporosis (IOP) who will receive 12M of romosozumab 210 mg monthly followed by 12M of denosumab 60 mg SC q6M. Aim 1 will define the within-group effects of this regimen. Aim 2 will compare results from participants treated with romosozumab-denosumab to the investigator's well-characterized historical controls treated with teriparatide followed by denosumab.