Shares of Dyne Therapeutics (NASDAQ:DYN) plunged 23% after the biotech firm announced changes to its regulatory strategy for DYNE-101, a treatment for myotonic dystrophy type 1 (DM1), following a recent Type C meeting with the U.S. Food and Drug Administration.
Although the FDA granted Breakthrough Therapy Designation to DYNE-101—highlighting its potential to address serious unmet medical needs—Dyne outlined an updated path to pursue Accelerated Approval. The revised clinical strategy is based on feedback from the FDA and new long-term data from the ongoing ACHIEVE trial.
Under the updated plan, Dyne has amended the protocol for the Registrational Expansion Cohort of the trial, designating video hand opening time (vHOT) as the primary efficacy endpoint. This marker will track the change in middle finger myotonia over six months versus placebo. Secondary goals include metrics such as splicing improvements, muscle strength, physical performance assessments, and patient-reported outcomes.
Enrollment for this expansion cohort is expected to wrap up by the fourth quarter of 2025, with topline results anticipated in mid-2026. If results are positive, Dyne aims to submit for U.S. Accelerated Approval by the end of that year. The company also plans to launch a confirmatory Phase 3 trial in early 2026.
The revised study will include 60 participants randomized in a 3:1 ratio to receive either DYNE-101 or a placebo. The trial builds on encouraging results from the earlier multiple ascending dose portion of ACHIEVE, which showed sustained improvements in myotonia and other clinical measures at 12 months for patients on the 6.8 mg/kg dose administered every eight weeks.
Financially, Dyne reported it had $677.5 million in cash, equivalents, and marketable securities as of March 31, 2025. The company expects this funding to support its operations through the fourth quarter of 2026.