Ultragenyx Pharmaceutical (NASDAQ:RARE) Phase 3 trials of setrusumab (UX143) in osteogenesis imperfecta failed to meet their primary endpoints, prompting the company to plan significant expense reductions while it evaluates next steps for the program.
The company, which trades on the Nasdaq under the ticker RARE, reported results dated Dec. 29, 2025, from the Orbit and Cosmic studies.
Neither trial demonstrated a statistically significant reduction in annualized clinical fracture rates, the primary endpoint, when compared with placebo in Orbit or bisphosphonates in Cosmic.
Both studies, however, met a key secondary endpoint, showing statistically significant improvements in bone mineral density versus their respective comparators.
Ultragenyx said safety findings were consistent with the established profile of setrusumab, with no new safety signals observed.
Ultragenyx said it will conduct additional analyses of other bone health and clinical endpoints from the trials to better define the future of the program.
In parallel, the company plans to implement significant expense reductions following the disappointing primary endpoint results.
Setrusumab has been a core late-stage asset in Ultragenyx’s pipeline for osteogenesis imperfecta, a rare genetic disorder characterized by fragile bones.
The company did not provide a timeline for potential regulatory discussions or further development decisions.