Overview

A class action lawsuit has been filed against Ultragenyx Pharmaceutical Inc., (“Ultragenyx,” or the “Company”) (NASDAQ : RARE) and certain of the Company’s senior executive officers (collectively, “Defendants”) alleging violations of federal securities laws. The Ultragenyx lawsuit is brought on behalf of all persons and entities who purchased or otherwise acquired Ultragenyx securities between August 3, 2023, and December 26, 2025, both dates inclusive (the “Class Period”). Investors have until April 6, 2026, to seek appointment as lead plaintiff of the Ultragenyx class action lawsuit.

Ultragenyx is a biopharmaceutical company focused on rare and ultrarare genetic disorders. The Company’s product candidates are typically in-licensed from partnerships or academic institutions. Pertinently, Ultragenyx is testing setrusumab for the treatment of Osteogenesis Imperfecta (“OI”), also known as brittle bone disease. Testing for setrusumab has proceeded to Phase III analysis through the Orbit and Cosmic studies, which are evaluating setrusumab’s ability to reduce patients’ annualized fracture rate. 

The complaint alleges Defendants made false and misleading statements and omissions of material facts concerning setrusumab’s effectiveness and the likelihood of success for the Phase III trials. Specifically, the Company repeatedly expressed confidence in: (1) setrusumab’s ability to trigger a decrease in annualized fracture rates among OI patients; and (2) the Phase III Orbit and Cosmic studies’ designs and likelihood of success. The complaint alleges that these positive statements were misleading because Defendants failed to disclose that increased bone mineral density did not necessarily correlate with reduced fracture rates and that the Phase III trial designs were unlikely to demonstrate the claimed benefits due to variability and control group performance.

The truth began to unravel on July 9, 2025, when Ultragenyx disclosed that the Phase III Orbit study failed to achieve statistical significance for the second interim analysis. On this news, Ultragenyx stock price fell $10.41 per share on July 10, 2025, a decline of approximately 25%.

The truth fully emerged on December 29, 2025, when Ultragenyx announced that both its Phase III Orbit and Cosmic studies had not “achieved statistical significance against the primary endpoints of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates, respectively.” The Company attributed the study failure to a “low fracture rate in the placebo group” of Orbit and a trend that fell shy of statistical significance in Cosmic. On this news, Ultragenyx stock plummeted, falling from a closing market price of $34.19 per share on December 26, 2025 to $19.72 per share on December 29, 2025, a decline of approximately 42%.

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If you purchased or otherwise acquired Ultragenyx securities between August 3, 2023, and December 26, 2025, and you wish to serve as lead plaintiff in this lawsuit, you are encouraged to submit your information to DiCello Levitt LLP via the form on this page. 

You can also contact DiCello Levitt attorneys Brian O’Mara or Hani Farah by calling (888) 287-9005 or at investors@dicellolevitt.com. 

The deadline to apply to the Court to serve as a lead plaintiff in the Ultragenyx lawsuit is April 6, 2026.