Dyne Therapeutics, Inc. ( DYN ) stock is trading lower after the company announced on Tuesday that it had revised the ongoing Registrational Expansion Cohort in the Phase 1/2 ACHIEVE trial for DYNE-101 for myotonic dystrophy type 1 (DM1).

The primary endpoint is a change from baseline in middle finger myotonia as measured by vHOT at 6 months, compared to placebo.

Video hand opening time (vHOT) measures hand function and myotonia (delayed relaxation of skeletal muscles after voluntary contraction).

Secondary endpoints include change from baseline in splicing as measured by the composite alternative splicing index (CASI-22), muscle strength as assessed by Quantitative Muscle Testing (QMT), performance on both the 10-Meter Walk/Run Test (10MWR) and 5 Times Sit to Stand Test (5xSTS), and the Myotonic Dystrophy Health Index (MDHI) patient-reported outcome measure, all at 6 months compared to placebo.

Also Read: JPMorgan Seeks Clarity On Dyne Therapeutics’ DYNE-101 Expansion, Regulatory Path

The cohort is expected to enroll 60 participants, randomized 3:1 to receive DYNE-101 6.8 mg/kg Q8W or placebo. Dyne plans to complete enrollment in the Registrational Expansion Cohort in the fourth quarter of 2025.

Dyne intends to use data from the Registrational Expansion Cohort and the already enrolled patients in the multiple ascending dose (MAD) and ongoing long-term extension portions of the ACHIEVE trial to support a potential submission for Accelerated Approval in the U.S.

Data from the cohort are planned for mid-2026 to support a potential U.S. Accelerated Approval submission in late 2026.

It seems that the company’s stock plunged as earlier Dyne expected to submit an Accelerated Approval Biologics License Application (BLA) in the first half of 2026.

Dyne plans to initiate a confirmatory Phase 3 clinical trial in Q1 2026.

Dyne also reported new long-term data from adult DM1 patients enrolled in the randomized, placebo-controlled MAD portion of the DYNE-101 ACHIEVE trial, including data from the 6.8 mg/kg Q8W cohort (n=6) at up to 12 months.

At the registrational dose of 6.8 mg/kg Q8W, DYNE-101 demonstrated robust and sustained improvement in myotonia as measured by vHOT and sustained improvements across multiple other endpoints.

As previously disclosed, treatment with DYNE-101 led to an improvement in vHOT of 3.3 seconds compared to placebo at 6 months.

New data demonstrated that mean improvements at 6 months were sustained at 12 months for vHOT, 10MWR, 5xSTS, MDHI, and QMT, which demonstrated a 10% improvement in strength at 6 months, increasing to 20% at 12 months relative to baseline.

The company expects that its $677.5 million cash, cash equivalents, and marketable securities as of March 31, 2025, will be sufficient to fund its operations into the fourth quarter of 2026.

The U.S. Food and Drug Administration (FDA) on Tuesday granted Breakthrough Therapy Designation to DYNE-101 for DM1.

Price Action: DYN stock is trading lower by 18.2% to $11.30 at last check Tuesday.

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