Ultragenyx Pharmaceutical ($RARE) Misleading Setrusumab Phase III Fracture-Rate Claims Case

N.D. California

Court

3:26-cv-01097

Case number

08/23/2023

Class period Start

12/26/2025

Class period End

04/06/2026

Lead Plaintiff motion deadline

$RARE investors filed a claim against Ultragenyx Pharmaceutical for allegedly misleading the market about the likelihood that its Phase III Orbit and Cosmic studies for setrusumab (UX143) would demonstrate a statistically significant reduction in annualized fracture rate (AFR) in osteogenesis imperfecta patients.
After the company disclosed setbacks in its Phase III program, $RARE fell 25.12% from $41.44 on July 9, 2025 to $31.03 on July 10, 2025.
Following the later disclosure that both Phase III studies failed their primary AFR endpoints, $RARE fell 42.32% from $34.19 on December 26, 2025 to $19.72 on December 29, 2025.
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Case Details:

Between August 3, 2023 and December 26, 2025, Ultragenyx told investors setrusumab was positioned to meaningfully reduce fractures in osteogenesis imperfecta, emphasizing strong Phase II signals (including bone mineral density gains) and expressing confidence that the Phase III Orbit and Cosmic designs would demonstrate a reduction in AFR, including through interim analyses.

However, during this period, investors allege the company overstated how reliably bone mineral density improvements would translate into reduced fracture rates and downplayed key risks and variability in the Phase III protocols—particularly the risk that the control group’s fracture rate could be too low (or otherwise confound the comparison), undermining the ability to show statistical significance on AFR.

Then, on July 9, 2025, Ultragenyx announced the Phase III Orbit study failed to achieve statistical significance at an interim checkpoint and that Orbit (and Cosmic) would continue toward final analysis. The stock fell about 25%, closing at $31.03 on July 10, 2025.

Additional revelations followed on December 29, 2025, when Ultragenyx disclosed that both Phase III Orbit and Cosmic failed to achieve statistical significance on their primary endpoints of reducing AFR (despite improvements in bone mineral density). By December 29, 2025, shares had dropped to $19.72, representing a total decline of 42.32% from $34.19 on December 26, 2025 over that correction window.

Based on these events, $RARE investors filed a claim against Ultragenyx Pharmaceutical Inc., alleging the company:
It concealed or downplayed key risks that Phase III variability and control-group fracture dynamics could prevent Orbit/Cosmic from demonstrating a statistically significant AFR benefit
It misrepresented the strength and predictability of the relationship between bone mineral density improvements and fracture-rate reduction in Phase III
It misled investors about Phase III success prospects, inflating $RARE’s stock price before corrective disclosures
Investors argue Ultragenyx misled the market about the true likelihood that setrusumab would meet the Phase III primary fracture-rate endpoints, causing losses when the study results and risks were revealed.

Case Type

US Securities Class Action

Case Status

Lead Plaintiff Appointment

Alleged Offence

Misleading Statements,

Financial Misrepresentation,

Fraud,

Failure to Disclose

Suspected Party

Directors,

Management

Security Type

Stocks

Trade Direction

Long

Shock Event Date

12/29/2025

Filing date

02/04/2026

Lead Plaintiff Deadline

04/06/2026

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