Class action lawsuits have been initiated against Ultragenyx Pharmaceutical and Mereo BioPharma following the December 29, 2025 announcement that their Phase III clinical trials for setrusumab failed to achieve primary endpoints in treating Osteogenesis Imperfecta. The ORBIT and COSMIC studies did not demonstrate the expected efficacy in reducing annualized fracture rates, prompting the legal action based on allegations that investors were misled about the trial outcomes.
The market reaction to the trial failures was severe, with Ultragenyx's stock price declining 42.32% and Mereo's American Depositary Shares falling 87.7% in the immediate aftermath of the announcement. These substantial losses have prompted investor groups to pursue legal remedies through coordinated class action proceedings.
Investors who held shares in either company during the relevant period are advised to note that lead plaintiff deadlines are set for April 6, 2026. Legal counsel specializing in securities litigation continues to evaluate the cases and welcomes contact from affected investors seeking information about their potential claims.