Kahn Swick & Foti, LLC (“KSF”), along with its partner and former Louisiana Attorney General Charles C. Foti, Jr., has alerted investors of Ultragenyx Pharmaceutical Inc. (“Ultragenyx” or the “Company”) about a filed class action securities lawsuit.

Class Definition: The legal action aims to recover losses for investors who purchased Ultragenyx securities and were negatively impacted by alleged securities fraud occurring between August 3, 2023, and December 26, 2025. Additional details are available at: https://www.ksfcounsel.com/cases/nasdaqgs-rare/

Investors can reach out to KSF Managing Partner Lewis Kahn by calling 1-877-515-1850 or by emailing lewis.kahn@ksfcounsel.com . More information can also be found on the case webpage linked above.

Case Details: On December 26, 2025, Ultragenyx released results from its Phase 3 Orbit and Cosmic trials evaluating setrusumab (UX143) for the treatment of osteogenesis imperfecta. The company reported that neither study achieved a statistically significant reduction in annualized fracture rates. Following this outcome, Ultragenyx stated it would reassess its operational plans and implement substantial cost-cutting measures.

After the announcement, Ultragenyx’s stock price dropped sharply—falling about 42% from $34.19 per share on December 26, 2025, to $19.72 per share on December 29, 2025.

The lawsuit is titled Steven Bailey v. Ultragenyx Pharmaceutical Inc., et al., Case No. 26-cv-01097.

What to Do: Investors who experienced losses during the specified period may seek appointment as lead plaintiff by April 6, 2026. However, participation in any potential recovery does not depend on serving in that role.

Why This Matters: Rosen Law Firm, a global firm specializing in investor rights, is reviewing possible securities claims on behalf of shareholders of Tandem Diabetes Care, Inc. (NASDAQ: TNDM). These claims stem from allegations that the company may have provided materially misleading information about its business operations to investors.

Potential Impact for Investors: If you purchased securities of Tandem Diabetes, you might qualify for compensation through a contingency fee arrangement, meaning you wouldn’t pay any upfront fees. Rosen Law Firm is preparing a class action lawsuit aimed at recovering losses for affected investors.

Next Steps: To become part of the potential class action, visit https://rosenlegal.com/submit-form/?case_id=19024, call Phillip Kim, Esq. toll-free at 866-767-3653, or email case@rosenlegal.com for more information.

Background: On August 7, 2025, before markets opened, Tandem Diabetes Care issued a press release titled “Tandem Diabetes Care Issues Voluntary Medical Device Correction for Select t:slim X2 Insulin Pumps.” The statement noted a voluntary correction for certain t:slim X2 insulin pumps to resolve a potential speaker-related issue that could disrupt insulin delivery. Following this announcement, Tandem Diabetes’ stock price dropped nearly 20% on the same day.

Why Choose Rosen Law Firm: Selecting experienced counsel with a proven track record is critical. Many firms sending notices lack the expertise, resources, or recognition in securities litigation. Rosen Law Firm focuses exclusively on securities class actions and shareholder derivative cases. The firm achieved the largest securities class action settlement ever against a Chinese company, has been ranked among the top four firms for settlements since 2013, and recovered hundreds of millions for investors—including $438 million in 2019 alone. Founder Laurence Rosen was named a Titan of the Plaintiffs’ Bar by Law360 in 2020, and multiple attorneys at the firm have been recognized by Lawdragon and Super Lawyers.

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Contact Information:
Laurence Rosen, Esq.
Phillip Kim, Esq.
The Rosen Law Firm, P.A.
275 Madison Avenue, 40th Floor
New York, NY 10016
Tel: (212) 686-1060 | Toll-Free: (866) 767-3653
Fax: (212) 202-3827
Email: case@rosenlegal.com
Website: www.rosenlegal.com