Key Takeaways:
Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) is facing at least five class-action lawsuits after clinical trial failures for its key drug candidate, setrusumab, triggered a more than 42 percent drop in its stock price.
According to a complaint filed by the Rosen Law Firm, defendants made "materially false and misleading statements" and failed to disclose adverse facts about setrusumab's potential to treat Osteogenesis Imperfecta, or OI. The lawsuit alleges the company's optimism was misplaced and that its study designs were unlikely to prove the drug's effectiveness in reducing fractures.
The lawsuits cover investors who purchased RARE securities between August 3, 2023, and December 26, 2025. The stock first plunged over 25 percent on July 9, 2025, when Ultragenyx revealed an interim analysis of its Phase III Orbit study failed to show a statistically significant benefit. The stock fell again, by more than 42 percent, on December 29, 2025, after the company announced both the Orbit and Cosmic studies failed to meet their primary endpoints.
The legal actions, brought by firms including The Schall Law Firm and Robbins Geller Rudman & Dowd LLP, seek to recover damages for investors. The core allegation is that Ultragenyx created a false impression of its understanding of setrusumab's effects, leading investors to purchase the stock at artificially inflated prices before the negative trial results were revealed.
The lawsuits center on the company's Phase III Orbit and Cosmic studies for setrusumab. While the drug was shown to increase bone mineral density, this did not translate to a statistically significant reduction in the annualized fracture rate for patients with OI, a rare genetic bone disorder.
The complaints argue that Ultragenyx based its optimistic public statements on a Phase II study that lacked a placebo control group, failing to account for the possibility that any observed benefit could be due to a placebo effect or an increased standard of care for participants. When the more rigorous Phase III trials failed, the company attributed the outcome to a "low fracture rate in the placebo group."
While the setrusumab program has stumbled, Ultragenyx has seen progress in other areas of its pipeline. The company recently announced the FDA accepted its Biologics License Application for UX111, a gene therapy for Sanfilippo syndrome Type A, and cleared its Investigational New Drug application for UX016 for GNE myopathy.
The lawsuits put Ultragenyx in a difficult position, facing significant legal and financial risk while trying to advance its other rare disease therapies. For investors, the immediate focus is the April 6, 2026, deadline to file a motion to serve as lead plaintiff in the class action.
This article is for informational purposes only and does not constitute investment advice.
