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Letters to Our Communities

December 8, 2025

Dear Duchenne Community:

Today, we are excited to announce positive topline results from the DELIVER clinical trial, along with new long-term data showing sustained benefits out to 24 months.

DELIVER is our global, randomized, placebo-controlled, double-blind, Phase 1/2 trial that evaluated the safety, tolerability and efficacy of zeleciment rostudirsen* (z-rostudirsen, also known as DYNE-251) in individuals with Duchenne muscular dystrophy (DMD) who have mutations in the DMD gene that are amenable to exon 51 skipping. DELIVER consists of two parts:

  • Part 1 was a multiple ascending dose (MAD) study, designed to identify the appropriate dose of z-rostudirsen to potentially treat DMD by testing different doses in small numbers of participants.

  • Part 2 was the Registrational Expansion Cohort (REC), designed to test the selected dose of z-rostudirsen in a larger number of participants to evaluate safety and efficacy. Trial participants who have completed the MAD and the REC continue to receive z-rostudirsen as part of the open label extension portion of the trial.

Below are key highlights, and our full press release with safety data and complete results can be found here.

Positive topline results from DELIVER Registrational Expansion Cohort (REC):

  • Dystrophin: The REC met its primary endpoint, demonstrating a statistically significant increase in dystrophin protein expression.

  • Function: Improvement relative to placebo was seen across all six prespecified endpoints at six months in this cohort of 32 participants. The six endpoints cover upper and lower limb function, as well as lung function.

New positive long-term results from DELIVER showed sustained functional improvement across multiple endpoints out to 24 months:

  • Sustained functional improvements from baseline were observed through 18 and 24 months in each of the six endpoints listed above for participants in the MAD cohort.

Favorable long-term safety and tolerability profile:

Safety and tolerability data were based on participants enrolled in the DELIVER trial and followed for up to 36 months, including participants initially enrolled in the MAD and REC and who have transitioned to the open label portions of the trial. Z-rostudirsen continued to demonstrate a favorable safety profile**, and most related treatment emergent adverse events (TEAEs) were mild or moderate. No related serious TEAEs were observed in the REC. Since the last safety update, two participants in the open label portions of the trial experienced malaise and/or pyrexia (fever) which were reported as related serious TEAEs. Both of these participants fully recovered and have continued to receive z-rostudirsen without interruption.

Next steps and timelines for z-rostudirsen (also known as DYNE-251):

  • We plan to submit a potential Biologics License Application (BLA) for U.S. Accelerated Approval in Q2 2026.

  • We plan to initiate a global Phase 3 clinical trial of z-rostudirsen in Q2 2026 to support global approvals.
  • We continue to expect a potential U.S. launch of z-rostudirsen in Q1 2027, assuming FDA grants Priority Review.
  • We also continue to pursue approval pathways outside of the U.S. for z-rostudirsen in patients with DMD who are amenable to exon 51 skipping.
  • The Dyne team understands the urgency, and we are working as quickly as possible to meet all of these critical milestones.

We look forward to continuing to share these data and program updates and welcome the opportunity to connect with the community via available channels.

Your insights and expertise have been vital in shaping our science and guiding the design of Dyne’s programs. We deeply appreciate the individuals and families who have devoted their time and trust to this clinical trial. Because of their unwavering commitment, we are able to move scientific understanding forward and drive progress in DMD drug development.

With gratitude and hope,

The Dyne Therapeutics Team

* z-rostudirsen is an investigational product and has not been approved by the FDA or any other regulatory authority for commercial use, and the safety and efficacy of z-rostudirsen has not been established.

** z-rostudirsen safety data as of August 19, 2025.

Rare Disease Day
AT DYNE WE SUPPORT ALL PEOPLE, FAMILIES AND CAREGIVERS LIVING WITH RARE DISEASES THIS RARE DISEASE DAY AND EVERY DAY
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