Setrusumab vs Placebo for Osteogenesis Imperfecta

Participants in Phase 2 will be randomized 1:1 to receive low dose or high dose setrusumab. Phase 2 participants will continue receiving their assigned dose of setrusumab until all Phase 2 participants have completed the Month 6 study visit. After this point, Phase 2 participants will begin receiving the selected dosing strategy in the Phase 2 open-label Treatment Extension Period. Phase 3 participants will be randomized 2:1 to receive setrusumab or placebo during the double-blind treatment period. Phase 3 participants will transition to the open-label Treatment Extension Period after the end of the double-blind period. Participants in the Phase 2 and Phase 3 treatment extension periods will receive open-label setrusumab treatment for at least 12 months, and have the option to remain in the open-label treatment period until setrusumab is commercially available in their region. An optional substudy will be conducted in approximately 10 participants (≥ 8 years) consisting of a bone biopsy to investigate the impact of setrusumab on bone histomorphology.