Dyne Therapeutics, Inc. announced that the U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy Designation to its investigational drug DYNE-101 for the treatment of myotonic dystrophy type 1 (DM1). The designation recognizes the therapy’s potential to offer significant improvement over existing treatments for this rare genetic muscle disorder.
The announcement follows a Type C meeting with the FDA and new long-term data from the company’s ongoing ACHIEVE clinical trial. Based on the meeting and positive feedback from regulators, Dyne has submitted a revised protocol for its Registrational Expansion Cohort to pursue U.S. Accelerated Approval for DYNE-101.
“This recognition by the FDA reinforces the therapeutic potential of DYNE-101,” said John Cox, CEO of Dyne Therapeutics. “Our updated data demonstrate sustained functional improvements in DM1 patients, and we’re working closely with the agency to bring this therapy to patients as efficiently as possible.”
The revised protocol designates video hand opening time (vHOT)—a measure of myotonia—as the primary endpoint for Accelerated Approval. Secondary endpoints include muscle strength via Quantitative Muscle Testing (QMT), mobility assessments, and patient-reported outcomes.
The expansion cohort will enroll 60 patients, randomized 3:1 to receive either DYNE-101 (6.8 mg/kg every 8 weeks) or placebo. Dyne expects to complete enrollment by the fourth quarter of 2025, with top-line data anticipated by mid-2026. A Phase 3 confirmatory trial is planned for early 2026.
New long-term results from the multiple ascending dose (MAD) portion of the ACHIEVE trial also support DYNE-101’s efficacy. In the 6.8 mg/kg group, patients experienced an average 3.3-second improvement in vHOT at 6 months compared to placebo. Improvements were maintained through 12 months across vHOT, QMT, the 10-Meter Walk/Run Test, 5 Times Sit to Stand Test, and the Myotonic Dystrophy Health Index (MDHI). Muscle strength gains rose from 10% at 6 months to 20% at 12 months.
Safety data from 56 participants showed that DYNE-101 continues to be well tolerated, with no treatment-related serious adverse events reported.
Dyne also confirmed its plans to pursue global regulatory pathways for DYNE-101.