The updated study will enroll 60 participants and track additional measures like muscle strength, mobility, and patient-reported outcomes.

Shares of Dyne Therapeutics fell on Tuesday after the company revised the primary endpoint in the registrational expansion cohort of its Achieve trial for DYNE-101, a treatment for myotonic dystrophy type 1 (DM1).

Dyne said it will now use video hand opening time (vHOT) as the primary endpoint, which measures the change from baseline in middle finger myotonia at six months compared to placebo. 

The update follows a Type C meeting with the U.S. Food and Drug Administration, which agreed vHOT could serve as an intermediate clinical endpoint to support a future submission for accelerated approval.

The revised protocol was submitted to the FDA earlier this month. 

Dyne plans to complete enrollment in the expansion cohort during the fourth quarter, with 60 participants randomized 3:1 to receive either DYNE-101 or placebo.

The revised expansion cohort will consist of 60 participants, randomized 3:1 to receive DYNE-101 at 6.8 mg/kg every eight weeks or placebo. 

Secondary endpoints include measures of muscle strength, walking performance, splicing biomarkers, and patient-reported outcomes. 

Enrollment is expected to be completed in Q4 2025, with pivotal data expected in mid-2026.

Data from the 12-month cohort of the MAD study showed sustained effects on all measures, including vHOT and strength testing, where patients improved by 20% from baseline. 

The company also reported a favorable safety profile, with no treatment-related serious adverse events in the 56 participants dosed to date.

Dyne plans to initiate a confirmatory Phase 3 trial in early 2026. 

It also reiterated that its cash balance of $677.5 million as of March 31 will fund operations into Q4 2026.

Stifel analyst Paul Matteis said the change “comes as a surprise” and “will raise questions,” though he maintained a ‘Buy’ rating on the stock, suggesting the move could offer a clearer approval route. 

Meanwhile, H.C. Wainwright called the change “encouraging,” noting that powering the trial to 60 participants could improve confidence in vHOT and help detect trends across secondary endpoints.

Chardan Capital also reiterated a ‘Buy’ rating and said the FDA’s confirmation of an accelerated pathway “more than offsets” a potential six-month delay to a Biologics License Application (BLA). 

The firm described the pullback as an “attractive entry point,” with the stock down 41% year-to-date.

On Stocktwits, retail sentiment was ‘bullish’ amid ‘extremely high’ message volume.

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