Major Class Action Lawsuit Filed Against Mereo BioPharma Group PLC (NASDAQ: MREO)

Philadelphia, February 09, 2026 — National plaintiffs’ law firm Berger Montague PC has announced the filing of a significant class action lawsuit against Mereo BioPharma Group plc, a biopharmaceutical company listed on the NASDAQ market under the ticker symbol MREO. The legal action was filed on behalf of investors who acquired Mereo American Depositary Shares (ADS) between June 5, 2023 and December 26, 2025 — a period now defined as the “Class Period.”

Who Can Participate in the Lawsuit?

Investors that purchased Mereo ADS during the Class Period now have the opportunity to participate in the lawsuit and may seek appointment as a lead plaintiff representative of the class. The deadline for all eligible investors to act is April 6, 2026. This deadline is critical for investors wishing to have a greater role in the litigation process.

Mereo BioPharma Group: Company Background

Mereo BioPharma Group plc is a London-headquartered biopharmaceutical company that focuses on developing therapies for rare diseases. Its business model centers on clinical research and development, particularly treatments intended to address serious genetic and metabolic disorders.

Among the treatments that drew significant investor attention were setrusumab therapies evaluated in the ORBIT and COSMIC clinical studies. These studies were designed to explore setrusumab’s effectiveness in treating Osteogenesis Imperfecta — a rare bone disorder characterized by brittle bones and frequent fractures.

Allegations in the Complaint

The class action complaint asserts that Mereo and certain company officers misled shareholders by publicly emphasizing positive investor expectations surrounding the ORBIT and COSMIC trials, while allegedly hiding critical information about their outcomes. According to the lawsuit, neither clinical study demonstrated statistically significant reductions in clinical fracture rates compared to control groups — the very measure many investors believed would validate the treatment’s effectiveness.

Impact on Mereo’s Stock Price

Following the disclosure of the disappointing clinical study results in late December 2025, Mereo’s ADS price suffered an abrupt and severe decline on the NASDAQ exchange. The company’s shares reportedly plummeted from a closing price of approximately $2.31 on December 26, 2025 to just $0.29 per share on December 29, representing a loss of more than 87.7% of market value in a single trading day.

This extraordinary drop wiped out billions of dollars in shareholder value, triggering a wave of investor concern and prompting multiple law firms to investigate potential legal claims on behalf of investors who suffered losses.

Legal Representation and Contact Information

If you are a Mereo BioPharma investor and wish to learn more about the class action lawsuit or your legal rights, Berger Montague PC has provided several contact points:

• Andrew Abramowitz — [email protected], (215) 875-3015
• Caitlin Adorni — [email protected], (267) 764-4865

The law firm is facilitating information and assistance for class members seeking counsel or wanting to file a claim.

About Berger Montague PC

Berger Montague PC is a prominent plaintiffs’ law firm in the United States that focuses on class actions, complex civil litigation, and mass torts in both federal and state courts. The firm has successfully represented clients in a wide array of practice areas, including securities litigation, consumer protection, antitrust, environmental law, employment issues, whistleblower cases, and more.

With more than $50 billion recovered for clients and class members over the past five decades, Berger Montague has established a reputation for high-profile litigation and substantial settlements. The firm’s headquarters are in Philadelphia, with additional offices across major U.S. cities and in Toronto, Canada.

Next Steps for Investors

Investors eligible to join the class action should consider consulting with legal counsel to understand their options before the April 6, 2026 deadline. Acting promptly is essential for anyone interested in seeking lead plaintiff status or otherwise participating in the litigation.

As multiple law firms continue to file related claims and investor alerts, the broader developments surrounding Mereo BioPharma’s legal challenges are expected to remain an important topic for shareholders and market observers alike.

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