- Submission for Accelerated Approval based on dystrophin as a surrogate endpoint -

- In the registrational expansion cohort of the DELIVER trial, treatment with z-rostudirsen resulted in a robust and statistically significant increase in dystrophin production with functional improvement observed across multiple clinical endpoints and a favorable safety profile¹ -

- Proposed dosing regimen of 20 mg/kg administered intravenously once every 4 weeks (Q4W) -

WALTHAM, Mass., May 26, 2026 (GLOBE NEWSWIRE) -- Dyne Therapeutics, Inc. (NASDAQ:DYN), a clinical-stage company focused on delivering functional improvement for people living with genetically driven neuromuscular diseases, today announced the submission of a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) for zeleciment rostudirsen (z-rostudirsen, also known as DYNE-251) 20 mg/kg Q4W for the treatment of individuals with Duchenne muscular dystrophy (DMD) amenable to exon 51 skipping.

"This is a significant milestone for both our company and the DMD community," said John Cox, president and chief executive officer of Dyne. "Despite the availability of approved therapies, there remains a significant unmet need in DMD for treatments with compelling efficacy, a favorable safety profile and improved dosing convenience. Z-rostudirsen was developed with the goal of delivering functional improvement with lower treatment burden for those living with this progressive disease. We look forward to continued engagement with the FDA to help facilitate a timely review, as we work toward bringing this potential best-in-class therapy to those in need as quickly as possible."

Dyne has requested Priority Review for the BLA, which, if granted, would shorten the review process from 10 months to 6 months following the FDA's 60-day filing review period. Dyne continues to expect a potential U.S. launch of z-rostudirsen in Q1 2027, assuming the FDA grants Priority Review and approval is received on the anticipated timeline.

In addition to z-rostudirsen, Dyne is advancing four development candidates (DYNE-253, DYNE-245, DYNE-244 and DYNE-255) for the potential treatment of DMD amenable to skipping of exons 53, 45, 44, and 55, respectively.

About Zeleciment Rostudirsen (z-rostudirsen, also known as DYNE-251)

Z-rostudirsen is an investigational therapeutic for individuals with DMD who have mutations in the DMD gene that are amenable to exon 51 skipping. The registrational expansion cohort of the global Phase 1/2 DELIVER clinical trial of z-rostudirsen met its primary endpoint. Data from the DELIVER trial served as the basis for a Biologics License Application (BLA) for potential U.S. Accelerated Approval. Z-rostudirsen continues to be evaluated in the long-term extension portion of the DELIVER trial and in the global confirmatory Phase 3 FORZETTO clinical trial. Z-rostudirsen consists of a phosphorodiamidate morpholino oligomer (PMO) conjugated to an antigen-binding fragment (Fab) that binds to the transferrin receptor 1 (TfR1). It is designed to enable the production of near-full length dystrophin in muscle and the central nervous system (CNS) to provide functional improvement. Z-rostudirsen has received Breakthrough Therapy, Fast Track and Rare Pediatric Disease designations from the U.S. Food and Drug Administration (FDA), as well as Orphan Drug designation from the FDA, European Medicines Agency (EMA) and the Ministry of Health, Labour and Welfare (MHLW) in Japan for the treatment of individuals with DMD amenable to exon 51 skipping.

In addition to z-rostudirsen, Dyne is building a DMD franchise and has preclinical programs targeting other exons, including DYNE-253, DYNE-245, DYNE-244 and DYNE-255.

About Duchenne Muscular Dystrophy (DMD)

Duchenne muscular dystrophy (DMD) is a rare X-linked progressive neuromuscular disorder caused by mutations in the DMD gene. These mutations result in a complete or near-complete absence of dystrophin, a protein critical for maintaining muscle structure and function. DMD is the most common form of childhood-onset muscular dystrophy, affecting approximately 12,000 individuals in the U.S. and 16,000 in the EU. Symptoms typically emerge between ages 3 and 5, beginning with muscle weakness in the upper arms, thighs and pelvic region, and progressively impacting the lower limbs, forearms, neck and trunk. In addition to physical decline, individuals may experience cognitive impairment and neuropsychiatric challenges such as intellectual disabilities, learning difficulties and behavioral disorders. Despite existing therapies, there remains a significant unmet need for new treatment options that deliver functional improvement.

About Dyne Therapeutics

Dyne Therapeutics is focused on delivering functional improvement for people living with genetically driven neuromuscular diseases. We are developing therapeutics that target muscle and the central nervous system (CNS) to address the root cause of disease. The company is advancing clinical programs for Duchenne muscular dystrophy (DMD) and myotonic dystrophy type 1 (DM1) as well as preclinical programs for facioscapulohumeral muscular dystrophy (FSHD), Pompe disease and multiple DMD mutations. At Dyne, we are on a mission to deliver functional improvement for individuals, families and communities. Learn more at https://www.dyne-tx.com/, and follow us on X, LinkedIn and Facebook.

Forward-Looking Statements

This press release contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this press release, including statements regarding Dyne's strategy, future operations, prospects and plans, objectives of management, the potential of the FORCE platform, the clinical and therapeutic potential of zeleciment rostudirsen (z-rostudirsen, also known as DYNE-251), the potential of z-rostudirsen to be a best-in-class therapy, expectations regarding the timing and outcome of interactions with regulatory authorities and the availability of the Accelerated Approval pathway for z-rostudirsen, the potential availability of Priority Review, and expectations regarding the timing of commercialization of z-rostudirsen, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "might," "objective," "ongoing," "plan," "predict," "project," "potential," "should," "will" or "would," or the negative of these terms, or other comparable terminology are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Dyne may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various important factors, including: uncertainties inherent in the identification and development of product candidates, including the initiation and completion of preclinical studies and clinical trials; uncertainties as to the availability and timing of results from preclinical studies and clinical trials; the timing of and Dyne's ability to enroll patients in clinical trials; uncertainties as to the FDA's and other regulatory authorities' interpretation of the data from Dyne's clinical trials and the regulatory approval process; whether Dyne's cash resources will be sufficient to fund its foreseeable and unforeseeable operating expenses and capital expenditure requirements; as well as the risks and uncertainties identified in Dyne's filings with the Securities and Exchange Commission (SEC), including the Company's most recent Form 10-Q and in subsequent filings Dyne may make with the SEC. In addition, the forward-looking statements included in this press release represent Dyne's views as of the date of this press release. Dyne anticipates that subsequent events and developments will cause its views to change. However, while Dyne may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing Dyne's views as of any date subsequent to the date of this press release.

Z-rostudirsen safety data as of August 19, 2025.

Contacts:

Investors

Mia Tobias

ir@dyne-tx.com

781-317-0353

Media

Stacy Nartker

snartker@dyne-tx.com

781-317-1938

Dyne Therapeutics Announces Submission of Biologics License Application (BLA) to U.S. FDA for Z-Rostudirsen in Exon 51 Duchenne Muscular Dystrophy (DMD)