# EDGAR Filing Document

**Accession Number:** 0001818794
**File Stem:** 0001193125-25-141739
**Filing Date:** 2025-6
**Character Count:** 53055
**Document Hash:** b5f905cbfc74267bd1038a53ff06b95d
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-141739.hdr.sgml**: 20250617

**ACCESSION NUMBER**: 0001193125-25-141739

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 44

**CONFORMED PERIOD OF REPORT**: 20250617

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Other Events

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20250617

**DATE AS OF CHANGE**: 20250617

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Dyne Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001818794
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 364883909
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-39509
- **FILM NUMBER:** 251051808

**BUSINESS ADDRESS:**
- **STREET 1:** 1560 TRAPELO ROAD
- **CITY:** WALTHAM
- **STATE:** MA
- **ZIP:** 02451
- **BUSINESS PHONE:** (781) 786-8230

**MAIL ADDRESS:**
- **STREET 1:** 1560 TRAPELO ROAD
- **CITY:** WALTHAM
- **STATE:** MA
- **ZIP:** 02451

?xml version='1.0' encoding='ASCII'? 8-K

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### WASHINGTON, D.C. 20549

### FORM 8-K

#### CURRENT REPORT

#### Pursuant to Section 13 or 15(d)

#### of the Securities Exchange Act of 1934

#### Date of report (Date of earliest event reported): June 17, 2025

## Dyne Therapeutics, Inc.

#### (Exact Name of Registrant as Specified in Charter)

---

| | | |
|:---|:---|:---|
| **Delaware** | **001-39509** | **36-4883909** |
| **(State or Other Jurisdiction**<br> **of Incorporation)** | **(Commission**<br> **File Number)** | **(IRS Employer**<br> **Identification No.)** |

---

---

| | |
|:---|:---|
| **1560 Trapelo Road**<br> **Waltham, Massachusetts** | **02451** |
| **(Address of Principal Executive Offices)** | **(Zip Code)** |

---

#### Registrant's telephone number, including area code: (781) 786-8230

#### Not applicable

#### (Former Name or Former Address, if Changed Since Last Report)
Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (*see* General Instruction A.2. below):

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

#### Securities registered pursuant to Section 12(b) of the Act:

---

| | | |
|:---|:---|:---|
| **Title of each class** | **Trading**<br> **symbol(s)** | **Name of each exchange**<br> **on which registered** |
| Common stock, $0.0001 par value per share | DYN | Nasdaq Global Select Market |

---

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

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---

| | |
|:---|:---|
| **Item 7.01.** | **Regulation FD Disclosure.**  |

---

On June 17, 2025, Dyne Therapeutics, Inc. (the "Company") issued a press release announcing that the U.S. Food and Drug Administration ("FDA") has granted Breakthrough Therapy Designation to DYNE-101 for the treatment of myotonic dystrophy type 1 ("DM1"). The Company also announced an updated plan for obtaining U.S. Accelerated Approval for DYNE-101 in DM1 following a Type C meeting with the FDA and analysis of new long-term functional data. A copy of the press release is furnished as Exhibit 99.1 hereto and is incorporated herein by reference.

The information furnished under this Item 7.01, including Exhibit 99.1, shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing.

---

| | |
|:---|:---|
| **Item 8.01.** | **Other Events.**  |

---

On June 17, 2025, the Company issued a press release announcing that the FDA has granted Breakthrough Therapy Designation to DYNE-101 for the treatment of DM1. The Company also announced an updated plan for obtaining U.S. Accelerated Approval for DYNE-101 in DM1 following a Type C meeting with the FDA and analysis of new long-term functional data.

#### Accelerated Approval Pathway for DYNE-101 in DM1
• In May 2025, the Company participated in a Type C meeting with the Center for Drug Evaluation and Research (CEDR) at the FDA and discussed the path to regulatory approval, including U.S. Accelerated Approval, for DYNE-101 in DM1.

• The Company and the FDA agreed that the next step toward Accelerated Approval was to submit for review the revised protocol for the Registrational Expansion Cohort of the ACHIEVE trial with video hand opening time ("vHOT") as the primary endpoint, to serve as an intermediate clinical endpoint.

• In June 2025, the Company submitted the revised protocol to the FDA.

• The Company has revised the ongoing Registrational Expansion Cohort in the ACHIEVE trial as follows:

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

• 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.

• This cohort is expected to enroll 60 participants, randomized 3:1 to receive DYNE-101 6.8 mg/kg once every eight weeks ("Q8W") or placebo.

• Additional clinical trial sites are being added, including sites in the U.S., to support enrollment.

• The Company intends to use data from the Registrational Expansion Cohort and from 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.

#### Accelerated Approval Milestones for DYNE-101 in DM1
• The Company plans to complete enrollment in the Registrational Expansion Cohort in the fourth quarter of 2025.

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

• The Company plans to initiate a confirmatory Phase 3 clinical trial in the first quarter of 2026.

• The Company is also pursuing expedited approval pathways globally for DYNE-101.

------

#### New Long-term Data from Multiple Ascending Dose Portion of ACHIEVE Trial
• The Company 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 as well as sustained improvements across multiple other endpoints.

• These data support improvement in vHOT as an early indicator of clinical benefit with DYNE-101 in DM1 and its potential as an intermediate clinical endpoint for U.S. Accelerated Approval.

• As previously disclosed, treatment with DYNE-101 led to an improvement in vHOT of 3.3 seconds as 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 also reported updated safety and tolerability data as of April 23, 2025 from 56 patients enrolled through the 6.8 mg/kg Q8W cohort of the ACHIEVE trial. DYNE-101 continued to demonstrate a favorable safety profile and no related serious treatment emergent adverse events have been identified.

#### Updated Cash Runway Guidance
On June 17, 2025, the Company also announced an update to its previously reported cash runway. The Company expects that its cash, cash equivalents and marketable securities as of March 31, 2025 will be sufficient to fund its operations into the fourth quarter of 2026. As previously reported, cash, cash equivalents and marketable securities were $677.5 million as of March 31, 2025.

#### Data Presentation
On June 17, 2025, the Company made available a presentation to be used with investors to discuss the updated plan for obtaining U.S. Accelerated Approval for DYNE-101 in DM1 and new long-term functional data from the ACHIEVE clinical trial. A copy of the presentation is filed as Exhibit 99.2 hereto and is incorporated herein by reference.

#### Cautionary Note Regarding Forward-Looking Statements
This Current Report on Form 8-K contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this Current Report on Form 8-K, including statements regarding the Company's strategy, future operations, prospects and plans, objectives of management, the potential of the FORCE platform and of DYNE-101, the anticipated timelines for reporting additional data from the ACHIEVE clinical trial and for the initiation of the planned phase 3 clinical trial in patients with DM1, initiating and enrolling both clinical trials, initiating additional clinical trials, and submitting applications for marketing approval, the availability of expedited approval pathways for DYNE-101, expectations regarding the outcome of interactions with regulatory authorities, and the sufficiency of the Company's cash resources for the period anticipated, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "might," "objective," "ongoing," "plan," "predict," "project," "potential," "should," or "would," or the negative of these terms, or other comparable terminology are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. The Company may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various important factors, including: uncertainties inherent in the identification and development of product candidates, including the initiation and completion of preclinical studies and clinical trials; uncertainties as to the availability and timing of results from preclinical studies and clinical trials; the timing of and the Company's ability to enroll patients in clinical trials; whether results from preclinical studies and data from clinical trials will be predictive of the final results of the clinical trials or other trials; whether data from clinical trials will support submission for regulatory approvals; uncertainties as to the FDA's and other regulatory authorities' interpretation of the data from the Company's clinical

------

trials and acceptance of the Company's clinical programs and as to the regulatory approval process for the Company's product candidates; whether the Company's cash resources will be sufficient to fund its foreseeable and unforeseeable operating expenses and capital expenditure requirements; as well as the risks and uncertainties identified in the Company's filings with the Securities and Exchange Commission ("SEC"), including the Company's most recent Form 10-Q and in subsequent filings the Company may make with the SEC. In addition, the forward-looking statements included in this Current Report on Form 8-K represent the Company's views as of the date hereof. The Company anticipates that subsequent events and developments will cause its views to change. However, while the Company may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing the Company's views as of any date subsequent to the date hereof.

---

| | |
|:---|:---|
| **Item 9.01.** | **Financial Statements and Exhibits.**  |

---

(d) Exhibits

---

| | |
|:---|:---|
| **Exhibit**<br> **No.** | **Description** |
| 99.1 | [Press Release, dated June 17, 2025.](d47489dex991.htm) |
| 99.2 | [Presentation, dated June 17, 2025.](d47489dex992.htm) |
| 104 | Cover Page Interactive Data File (embedded within the Inline XBRL document) |

---

------

#### SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

---

| | | |
|:---|:---|:---|
|  | DYNE THERAPEUTICS, INC. | DYNE THERAPEUTICS, INC. |
| Date: June 17, 2025 | By: | /s/ John G. Cox |
|  | Name: | John G. Cox |
|  | Title: | President and Chief Executive Officer |

---

## Exhibit 99.1

**Exhibit 99.1**![LOGO](g47489g0617003700384.jpg)

**Dyne Therapeutics Announces FDA Breakthrough Therapy Designation for DYNE-101 and Updated Plan for Accelerated Approval in DM1 Following Type C Meeting** 

*- Based on Type C meeting and new data, Dyne submitted revised ACHIEVE trial protocol to FDA elevating vHOT to primary endpoint for U.S. Accelerated Approval -* 

*- New positive clinical data from Phase 1/2 ACHIEVE trial support vHOT as early indicator of clinical benefit with DYNE-101 in DM1 -* 

*- Ongoing Registrational Expansion Cohort in ACHIEVE trial to enroll 60 participants and include sites in U.S. -* 

*- Company to host an investor and analyst conference call today, June 17, at 8:00 a.m. ET -* 

**WALTHAM, Mass., June 17, 2025** – <u>Dyne Therapeutics, Inc.</u> (Nasdaq: DYN), a clinical-stage company focused on delivering functional improvement for people living with genetically driven neuromuscular diseases, today announced that the U.S. Food and Drug Administration (FDA) has granted Breakthrough Therapy Designation to DYNE-101 for the treatment of myotonic dystrophy type 1 (DM1). The company also announced an updated plan for obtaining U.S. Accelerated Approval for DYNE-101 in DM1 following a Type C meeting with the FDA and analysis of new long-term functional data.

"After our Type C meeting, we were granted Breakthrough Therapy Designation for DYNE-101 in DM1. We appreciate the FDA's active engagement and guidance as we advance this promising program through the Accelerated Approval pathway in the U.S.," said John Cox, president and chief executive officer of Dyne. "Based on feedback from the FDA, along with our 6-month and new 12-month efficacy data, we have submitted a revised protocol for the ongoing Registrational Expansion Cohort of the ACHIEVE trial with vHOT as the primary endpoint for potential Accelerated Approval."

**Accelerated Approval Pathway for DYNE-101 in DM1** 

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• In May 2025, Dyne participated in a Type C meeting with the Center for Drug Evaluation and Research (CDER) at the
FDA and discussed the path to regulatory approval, including U.S. Accelerated Approval, for DYNE-101 in DM1.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dyne and FDA agreed that the next step toward Accelerated Approval was to submit for review the revised protocol
for the Registrational Expansion Cohort of the ACHIEVE trial with video hand opening time (vHOT) as the primary endpoint, to serve as an intermediate clinical endpoint.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• In June, Dyne submitted the revised protocol to the FDA.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dyne has revised the ongoing Registrational Expansion Cohort in the ACHIEVE trial as follows:

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

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• 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.

------

![LOGO](g47489g0617003700384.jpg)

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• This cohort is expected to enroll 60 participants, randomized 3:1 to receive DYNE-101 6.8 mg/kg Q8W or placebo.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Additional clinical trial sites are being added, including sites in the U.S., to support enrollment.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dyne intends to use data from the Registrational Expansion Cohort and from 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.

**Accelerated Approval Milestones for DYNE-101 in DM1** 

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dyne plans to complete enrollment in the Registrational Expansion Cohort in Q4 2025.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Data from this cohort are planned for mid-2026 to support a potential
U.S. Accelerated Approval submission in late 2026.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dyne plans to initiate a confirmatory Phase 3 clinical trial in Q1 2026.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dyne is also pursuing expedited approval pathways globally for DYNE-101.

**New Long-term Data from Multiple Ascending Dose (MAD) Portion of ACHIEVE Trial** 

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Today, Dyne 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.

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

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• These data support improvement in vHOT as an early indicator of clinical benefit with DYNE-101 in DM1 and its potential as an intermediate clinical endpoint for U.S. Accelerated Approval.

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

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• 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.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dyne also reported updated safety and tolerability data<sup>1</sup>
from 56 patients enrolled through the 6.8 mg/kg Q8W cohort of the ACHIEVE trial. DYNE-101 continued to demonstrate a favorable safety profile, and no related serious treatment emergent adverse events have been
identified.

**Updated Cash Runway Guidance** 

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

**Investor Conference Call** 

Dyne will host a conference call and webcast to discuss these updates today, June 17, 2025, at 8:00 a.m. ET and a replay will be accessible for 90 days following the presentation. An accompanying slide presentation for the event and an updated corporate presentation will also be available. To access these presentations and register for the webcast and replay, please visit the Investors & Media section of Dyne's website at <u>https://investors.dyne-tx.com/news-and-events/events-and-presentations</u>.

------

![LOGO](g47489g0617003700384.jpg)

**About U.S. FDA Accelerated Approval** 

Accelerated Approval allows the FDA to approve drugs for serious conditions with an unmet medical need based on a surrogate or intermediate clinical endpoint, which is reasonably likely to predict clinical benefit.

**About Breakthrough Therapy Designation** 

The FDA grants Breakthrough Therapy Designation to expedite the development and review of drugs that are intended to treat a serious condition with preliminary clinical evidence indicating that the drug may demonstrate substantial improvement over available therapy on one or more clinically significant endpoints. This designation offers benefits to DYNE-101 in the U.S. including:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Enhanced FDA support, including senior-level involvement to guide efficient development as well as
decision-making

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Early and frequent communication with FDA reviewers on trial design and regulatory strategy

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Rolling and Priority Review eligibility, potentially reducing the BLA review timeline from 12 to 8
months

**About DYNE-101**

DYNE-101 is an investigational therapeutic being evaluated in the Phase 1/2 global ACHIEVE clinical trial for people living with DM1. DYNE-101 consists of an antisense oligonucleotide (ASO) conjugated to a fragment antibody (Fab) that binds to the transferrin receptor 1 (TfR1) to enable delivery to muscle and the central nervous system. It is designed to promote functional improvement in individuals living with DM1 by reducing toxic nuclear *DMPK* RNA and correcting the spliceopathy underlying the disease. DYNE-101 has been granted Orphan drug, Fast Track and Breakthrough Therapy designations by the U.S. Food and Drug Administration and Orphan drug designation by the European Medicines Agency for the treatment of DM1.

**About Myotonic Dystrophy Type 1 (DM1)**

DM1 is a rare, progressive, genetic disease that affects skeletal, cardiac and smooth muscle in addition to the central nervous system (CNS). It is a monogenic, autosomal dominant disease caused by an abnormal trinucleotide expansion in a region of the *DMPK* gene. This expansion of CTG repeats causes toxic RNA to cluster in the nucleus, forming nuclear foci and altering the splicing of multiple proteins essential for normal cellular function. This altered splicing, or spliceopathy, results in a wide range of symptoms. People living with DM1 typically experience myotonia and progressive weakness of major muscle groups, which can affect mobility, breathing, heart function, speech, digestion and vision. Cognitive dysfunction may manifest as fatigue, excessive daytime sleepiness, an apathic temperament and brain fog. DM1 is estimated to affect more than 40,000 people in the United States and over 74,000 people in Europe, but there are currently no approved disease-modifying therapies.

------

![LOGO](g47489g0617003700384.jpg)

**About Dyne Therapeutics** 

Dyne Therapeutics is focused on delivering functional improvement for people living with genetically driven neuromuscular diseases. We are developing therapeutics that target muscle and the central nervous system (CNS) to address the root cause of disease. The company is advancing clinical programs for myotonic dystrophy type 1 (DM1) and Duchenne muscular dystrophy (DMD), and preclinical programs for facioscapulohumeral muscular dystrophy (FSHD) and Pompe disease. At Dyne, we are on a mission to deliver functional improvement for individuals, families and communities. Learn more <u>https://www.dyne-tx.com/</u>, and follow us on <u>X</u>, <u>LinkedIn</u> and <u>Facebook</u>.

**Forward-Looking Statements** 

This press release contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this press release, including statements regarding Dyne's strategy, future operations, prospects and plans, objectives of management, the potential of the FORCE platform and of DYNE-101, the anticipated timelines for reporting additional data from the ACHIEVE clinical trial and for the initiation of the planned phase 3 clinical trial in patients with DM1, initiating and enrolling both clinical trials, initiating additional clinical trials, and submitting applications for marketing approval, the availability of expedited approval pathways for DYNE-101, expectations regarding the outcome of interactions with regulatory authorities, and the sufficiency of Dyne's cash resources for the period anticipated, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "might," "objective," "ongoing," "plan," "predict," "project," "potential," "should," or "would," or the negative of these terms, or other comparable terminology are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Dyne may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various important factors, including: uncertainties inherent in the identification and development of product candidates, including the initiation and completion of preclinical studies and clinical trials; uncertainties as to the availability and timing of results from preclinical studies and clinical trials; the timing of and Dyne's ability to enroll patients in clinical trials; whether results from preclinical studies and data from clinical trials will be predictive of the final results of the clinical trials or other trials; whether data from clinical trials will support submission for regulatory approvals; uncertainties as to the FDA's and other regulatory authorities' interpretation of the data from Dyne's clinical trials and acceptance of Dyne's clinical programs and as to the regulatory approval process for Dyne's product candidates; whether Dyne's cash resources will be sufficient to fund its foreseeable and unforeseeable operating expenses and capital expenditure requirements; as well as the risks and uncertainties identified in Dyne's filings with the Securities and Exchange Commission (SEC), including the company's most recent Form 10-Q and in subsequent filings Dyne may make with the SEC. In addition, the forward-looking statements included in this press release represent Dyne's views as of the date of this press release. Dyne anticipates that subsequent events and developments will cause its views to change. However, while Dyne may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing Dyne's views as of any date subsequent to the date of this press release.

------

![LOGO](g47489g0617003700384.jpg)

1. DYNE-101 safety data as of April 23, 2025

**Contacts:** 

**Investors** 

Mia Tobias

<u>ir@dyne-tx.com</u>

781-317-0353

**Media** 

Stacy Nartker

<u>snartker@dyne-tx.com</u> 

781-317-1938

## Exhibit 99.2

![Slide 1](g47489ex99_2s1g1.jpg)

Advancing Functional Improvement in DM1 DYNE-101 U.S. Accelerated Approval and Clinical Update JUNE 17, 2025 Exhibit 99.2

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![Slide 2](g47489ex99_2s2g1.jpg)

Forward-Looking Statements & Disclaimer This presentation contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this presentation, including statements regarding Dyne's strategy, future operations, prospects and plans, objectives of management, the potential of the FORCE platform, the therapeutic potential of DYNE-101 and DYNE-251, the anticipated timelines for reporting additional data from the ACHIEVE and DELIVER clinical trials and initiating and enrolling registrational cohorts and the planned Phase 3 clinical trial in patients with DM1, expectations regarding the timing and outcome of interactions with global regulatory authorities and the availability of accelerated approval pathways for DYNE-101 and DYNE-251, and expectations regarding the timing of filing applications for U.S. Accelerated Approval and the sufficiency of Dyne's cash resources for the period anticipated, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "might," "objective," "ongoing," "plan," "predict," "project," "potential," "should," or "would," or the negative of these terms, or other comparable terminology are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Dyne may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various important factors, including: uncertainties inherent in the identification and development of product candidates, including the initiation and completion of preclinical studies and clinical trials; uncertainties as to the availability and timing of results from preclinical studies and clinical trials; the timing of and Dyne's ability to enroll patients in clinical trials; whether results from preclinical studies and initial data from early clinical trials will be predictive of the final results of the clinical trials or future trials; uncertainties as to the FDA's and other regulatory authorities' interpretation of the data from Dyne's clinical trials and acceptance of Dyne's clinical programs and the regulatory approval process; whether Dyne's cash resources will be sufficient to fund its foreseeable and unforeseeable operating expenses and capital expenditure requirements; as well as the risks and uncertainties identified in Dyne's filings with the Securities and Exchange Commission (SEC), including the Company's most recent Form 10-Q and in subsequent filings Dyne may make with the SEC. In addition, the forward-looking statements included in this presentation represent Dyne's views as of the date of this presentation. Dyne anticipates that subsequent events and developments will cause its views to change. However, while Dyne may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing Dyne's views as of any date subsequent to the date of this presentation. This presentation also contains estimates, projections and other statistical data made by independent parties and by the Company relating to market size and growth and other data about the Company's industry and business. This data involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. The Company has not independently verified the accuracy and completeness of the information obtained by third parties included in this presentation. In addition, projections, assumptions and estimates of the Company's future performance and the future performance of the markets in which the Company operates are necessarily subject to a high degree of uncertainty and risk.

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Program Closing Remarks John Cox, President & CEO Updated Plan for U.S. Accelerated Approval and New Clinical Data for DYNE-101 Doug Kerr, M.D., Ph.D., Chief Medical Officer Opening Remarks John Cox, President & CEO Available for Q&A Erick Lucera, Chief Financial Officer

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Today's Update 1. Safety data as of April 23, 2025; vHOT = video hand opening time; MAD = multiple ascending dose; LTE = long-term extension. Breakthrough Therapy Designation Accelerated Approval Pathway with vHOT New Long-Term Data from ACHIEVE Trial FDA granted Breakthrough Therapy Designation for DYNE-101 in DM1 following Type C Meeting Dyne and FDA agreed that the next step toward Accelerated Approval was to submit for review the revised protocol for the Registrational Expansion Cohort of the ACHIEVE trial with vHOT as primary endpoint Revised protocol submitted to FDA in June Robust and sustained functional improvement across multiple measures at 6 and 12 months at registrational dose Data support vHOT improvement as early indicator of clinical benefit with DYNE-101 Continued favorable safety profile1 Data from Registrational Expansion Cohort, MAD, and LTE portions of ACHIEVE trial intended to support a potential U.S. Accelerated Approval Data from the Registrational Expansion Cohort are planned for mid-2026 to support a potential U.S. Accelerated Approval submission in late 2026

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Program Closing Remarks John Cox, President & CEO Updated Plan for U.S. Accelerated Approval and New Clinical Data for DYNE-101 Doug Kerr, M.D., Ph.D., Chief Medical Officer Opening Remarks John Cox, President & CEO Available for Q&A Erick Lucera, Chief Financial Officer

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Restore normal RNA splicing to achieve functional improvement for those living with DM1 Functional Improvement via Splicing Correction in Nucleus OUR APPROACH Mutation in the DMPK gene leads to mis-splicing of multiple genes Onset at any point, depending on DM1 phenotype Life expectancy of 45 - 60 years Overview >40,000 (US) >74,000 (Europe) Population Muscle weakness & myotonia CNS manifestations including fatigue, cognition, and sleep Gastrointestinal issues Cardiac arrhythmia Pulmonary abnormalities Clinical Presentation NO approved therapies DM1 is a Devastating Neuromuscular Splicing Disorder Note: DM1 = myotonic dystrophy type 1; CNS = central nervous system.

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DYNE-101 Addressing the Central Pathobiology of DM1 to Enable Broad Functional Improvement1 Muscle Strength: Quantitative Muscle Testing Functional Assessments: 10-Meter Walk / Run; 5 Times Sit to Stand Patient Reported Outcomes: Myotonic Dystrophy Health Index (MDHI) Robust and widespread delivery DMPK degradation in the nucleus MBNL release and splicing correction MBNL trapped: Splicing defect CUG expansion MBNL released: Splicing corrected Differentiated MOA DYNE-101 Myotonia: Video Hand Opening Time (vHOT) DMPK Early clinical effect DYNE-101 1. Image depicts the intended DYNE-101 mechanism of action (MOA); DM1 = myotonic dystrophy type 1. Broad functional improvement

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Revised Registrational Expansion Cohort to Support Potential U.S. Accelerated Approval ACHIEVE MAD cohorts complete; all cohorts now at 6.8 mg/kg Q8W in long-term / open label extension ACHIEVE Registrational Expansion Cohort currently enrolling Primary endpoint: Change from baseline in middle finger myotonia as measured by vHOT at 6 months compared to placebo1 Secondary endpoints include: CASI-22, QMT, 10MWR, 5xSTS, and MDHI at 6 months Global footprint, including addition of U.S. sites N=60 3:1 randomization DYNE-101 6.8 mg/kg Q8W Placebo ACHIEVE Long-term / Open Label Extension 6 months Registrational Expansion Cohort Q8W dosing continues Data planned for mid-2026 to support a potential Accelerated Approval submission in late 2026 1. Average baseline vHOT for the 56 patients enrolled in the multiple ascending dose portion of ACHIEVE was 9.2 seconds. MAD = multiple ascending dose; CASI-22 = composite alternative splicing index; vHOT = video hand opening time; QMT = quantitative muscle testing; 10MWR = 10-meter walk/run test; 5xSTS = 5 times sit to stand test; MDHI = Myotonic Dystrophy Health Index.

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New Data Support the Potential for Accelerated Approval of DYNE-101 with vHOT as Primary Endpoint Intermediate clinical endpoint DYNE-101 Outcomes DYNE-101 Safety Data A clinical measure with the potential to detect a drug effect earlier than other clinically meaningful endpoints and which is considered reasonably likely to predict clinical benefit Data support improvement in vHOT as early indicator of clinical benefit with DYNE-101 Sustained improvements increase confidence in 6-month results Favorable safety profile1 Accelerated Approval allows FDA to approve drugs for serious conditions with an unmet medical need based on a surrogate or intermediate clinical endpoint, which is reasonably likely to predict clinical benefit 1. Safety data as of April 23, 2025; vHOT = video hand opening time.

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New Data Support the Potential for Accelerated Approval of DYNE-101 with vHOT as Primary Endpoint Intermediate clinical endpoint DYNE-101 Outcomes DYNE-101 Safety Data Data support improvement in vHOT as early indicator of clinical benefit with DYNE-101 Sustained improvements increase confidence in 6-month results Favorable safety profile1 Accelerated Approval allows FDA to approve drugs for serious conditions with an unmet medical need based on a surrogate or intermediate clinical endpoint, which is reasonably likely to predict clinical benefit A clinical measure with the potential to detect a drug effect earlier than other clinically meaningful endpoints and which is considered reasonably likely to predict clinical benefit 1. Safety data as of April 23, 2025; vHOT = video hand opening time.

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Data Support vHOT Improvement as an Early Indicator of Clinical Benefit with DYNE-101 vHOT Change from Baseline at 6 Months Placebo Month 6 (N=14) 6.8 mg/kg Q8W Month 12 (N=6) Improvement With DYNE-101, all participants at highest 3 doses who improved in 6M vHOT improved in 12M strength, 5xSTS, and/or 10MWR Notes: Mixed model for repeated measures (MMRM): fixed effects: dose, visit, baseline, dose by visit interaction, baseline by visit interaction. Data: all dose groups except recovery group; excluding placebo data after 6 months; Data presented are least squares (LS) mean change from baseline ± SEM (standard error of the mean); 6 months = 169 days, 12 months = 337 days; vHOT = video hand opening time; QMT = quantitative muscle testing; 10MWR = 10-meter walk/run test; 5xSTS = 5 times sit to stand test; MDHI = Myotonic Dystrophy Health Index; %p = percent predicted. Favors DYNE-101

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A clinical measure with the potential to detect a drug effect earlier than other clinically meaningful endpoints and which is considered reasonably likely to predict clinical benefit New Data Support the Potential for Accelerated Approval of DYNE-101 with vHOT as Primary Endpoint Intermediate clinical endpoint DYNE-101 Outcomes DYNE-101 Safety Data Data support improvement in vHOT as early indicator of clinical benefit with DYNE-101 Sustained improvements increase confidence in 6-month results Favorable safety profile1 Accelerated Approval allows FDA to approve drugs for serious conditions with an unmet medical need based on a surrogate or intermediate clinical endpoint, which is reasonably likely to predict clinical benefit 1. Safety data as of April 23, 2025; vHOT = video hand opening time.

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Robust and Sustained vHOT Improvement at 6 and 12 Months vHOT Middle Finger Improvement 1. vHOT Middle Finger (sec) is the average of all myotonia trials for an individual participant in ACHIEVE; vHOT = video hand opening time; SEM = standard error of the mean; BL = baseline. 3 months = 85 days; 6 months = 169 days; 12 months = 337 days.

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Strength Continues to Improve from Month 6 to Month 12 Quantitative Muscle Testing (QMT) Total Score Improvement SEM = standard error of the mean; BL = baseline; %p = percent predicted; 3 months = 85 days; 6 months = 169 days; 12 months = 337 days.

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Robust Benefit Across Multiple Timed Function Tests Sustained at 6 and 12 Months 5 Times Sit to Stand Test Improvement SEM = standard error of the mean; BL = baseline; 3 months = 85 days; 6 months = 169 days; 12 months = 337 days. 10-Meter Walk/Run Test

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Myotonic Dystrophy Health Index (MDHI) Total Score Improvement Deep Improvement in Patient Reported Outcome Sustained at 6 and 12 Months SEM = standard error of the mean; BL = baseline; 3 months = 85 days; 6 months = 169 days; 12 months = 337 days.

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Cognitive Impairment Communication Emotional Issues Sleep Pain Fatigue Improvement Subscale Change from Baseline (Mean +/- SEM) SEM = standard error of the mean; BL = baseline; Patient-reported outcomes (PRO) including Myotonic Dystrophy Health Index (MDHI) collected at baseline, 6 months (169 days) and 12 months (337 days). Sustained Improvement in CNS-related MDHI Subscales Over Time

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A clinical measure with the potential to detect a drug effect earlier than other clinically meaningful endpoints and which is considered reasonably likely to predict clinical benefit New Data Support the Potential for Accelerated Approval of DYNE-101 with vHOT as Primary Endpoint Intermediate clinical endpoint DYNE-101 Outcomes DYNE-101 Safety Data Data support improvement in vHOT as early indicator of clinical benefit with DYNE-101 Sustained improvements increase confidence in 6-month results Favorable safety profile1 Accelerated Approval allows FDA to approve drugs for serious conditions with an unmet medical need based on a surrogate or intermediate clinical endpoint, which is reasonably likely to predict clinical benefit 1. Safety data as of April 23, 2025; vHOT = video hand opening time.

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TEAE Category Participants with ≥1 TEAE – n (%) 1.8 mg/kg Q4W+Rec. N=16 3.4 mg/kg Q4W+Rec. N=16 3.4 mg/kg Q8W N=8 5.4 mg/kg Q8W N=8 6.8 mg/kg Q8W N=8 Overall (N=56) Any TEAE 16 (100%) 16 (100%) 8 (100%) 8 (100%) 8 (100%) 56 (100%) Any related TEAE 9 (56%) 10 (63%) 3 (38%) 6 (75%) 6 (75%) 34 (61%) Any serious TEAE 4 (25%) 0 1 (13%) 0 0 5 (9%) Any serious related TEAE 0 0 0 0 0 0 Any TEAE leading to withdrawal from study 0 0 0 0 0 0 Any TEAE leading to death 0 0 0 0 0 0 Most TEAEs Were Mild or Moderate in Intensity1 6 serious TEAEs unrelated to study drug Atrioventricular block first degree (1)2 Pneumonia (2 events in same participant) Pulmonary embolism (1)3 Hyponatremia (1) Influenza (1) Most common TEAEs (≥20% participant incidence)4 Nasopharyngitis (41%) Procedural pain (34%) Influenza (30%) Infusion-related reaction (29%) Headache (27%) Diarrhea (23%) Additional Safety Data Liver enzyme elevations have been observed in a minority of participants No impact on liver function (bilirubin or coagulation) Interpretation is complicated by underlying disease and elevated baseline values up to ~2.5x greater than the upper limit of normal No participants have demonstrated persistent related anemia or thrombocytopenia DYNE-101: Favorable Safety Profile with No Serious Related TEAEs Summary of Treatment Emergent Adverse Events (TEAEs)1 1. Data as of April 23, 2025; 2. Transient worsening of atrioventricular (AV) block in a participant with ongoing medical history of first-degree AV block; 3. Attributed to risk factors for pulmonary embolism; 4. All cohorts combined; preferred terms are reported.

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vHOT is the Primary Endpoint to Support Potential Accelerated Approval of DYNE-101 Myotonia is an early and common sign of DM1 Data support vHOT as early indicator of clinical benefit with DYNE-101 DYNE-101 has demonstrated robust improvement in vHOT as early as 3 months Myotonia First symptom1 38.3% Prevalence2 88% 1. Hilbert JE, et al. J Neurol 2013;260:2497-2504. N = 679 people with DM1 enrolled in the US National Registry. 2. Hagerman KA, et al. Muscle Nerve 2019;59:457-464. Data from the Christopher Project. N = 457 for DM1. DM1 = myotonic dystrophy type 1; vHOT = video hand opening time; SEM = standard error of the mean. Improvement

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Demonstrated Proof of Concept in MAD and LTE Comprehensive Development Program for DYNE-101 in DM1 Registrational Expansion Cohort to Support U.S. Accelerated Approval Planned Phase 3 Study ü Selected registrational dose of 6.8 mg/kg Q8W Data support vHOT improvement as early indicator of clinical benefit with DYNE-101 ü Potential best-in-class profile across myotonia, strength, timed function tests, and patient reported outcomes, including CNS-related ü Favorable safety profile1; no serious related TEAEs ü 60 participants (3:1); 6.8 mg/kg Q8W Primary endpoint: Change from baseline in middle finger myotonia as measured by vHOT at 6 months, compared to placebo Secondary endpoints include: CASI-22, QMT, 10MWR, 5xSTS, and MDHI at 6 months Planning to initiate confirmatory Phase 3 clinical trial in Q1 2026 1. Safety data as of April 23, 2025; DM1 = myotonic dystrophy type 1; MAD = multiple ascending dose; LTE = long term extension; CASI-22 = composite alternative splicing index; vHOT = video hand opening time; 10MWR = 10-meter walk/run test; QMT = quantitative muscle testing; 5xSTS = 5 times sit to stand test; MDHI = myotonic dystrophy health index. Updated protocol submitted to FDA Enrollment completion planned for Q4 2025 Ongoing engagement with global regulators to finalize trial design Data planned for mid-2026 to support potential U.S. Accelerated Approval submission in late 2026

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Program Updated Plan for U.S. Accelerated Approval and New Clinical Data for DYNE-101 Doug Kerr, M.D., Ph.D., Chief Medical Officer Opening Remarks John Cox, President & CEO Available for Q&A Erick Lucera, Chief Financial Officer Closing Remarks John Cox, President & CEO

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Summary 1. Safety data as of April 23, 2025; vHOT = video hand opening time; MAD = multiple ascending dose; LTE = long-term extension. Breakthrough Therapy Designation Accelerated Approval Pathway with vHOT New Long-Term Data from ACHIEVE Trial FDA granted Breakthrough Therapy Designation for DYNE-101 in DM1 following Type C Meeting Dyne and FDA agreed that the next step toward Accelerated Approval was to submit for review the revised protocol for the Registrational Expansion Cohort of the ACHIEVE trial with vHOT as primary endpoint Revised protocol submitted to FDA in June Robust and sustained functional improvement across multiple measures at 6 and 12 months at registrational dose Data support vHOT improvement as early indicator of clinical benefit with DYNE-101 Continued favorable safety profile1 Data from Registrational Expansion Cohort, MAD, and LTE portions of ACHIEVE trial intended to support a potential U.S. Accelerated Approval Data from the Registrational Expansion Cohort are planned for mid-2026 to support a potential U.S. Accelerated Approval submission in late 2026

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Building Momentum Toward Two Potential Launches in 2027 DYNE-101 for DM1 DYNE-251 for Exon 51 DMD Q4 2025 Complete enrollment planned for Registrational Expansion Cohort Q1 2025 Completed enrollment of Registrational Expansion Cohort Mid-2026 Data planned for Registrational Expansion Cohort Late 2025 Data planned for Registrational Expansion Cohort Late 2026 Potential submission for U.S. Accelerated Approval Early 2026 Potential submission for U.S. Accelerated Approval 2027 Potential U.S. launch 2027 Potential U.S. launch 1st potential launch for Dyne DM1 = myotonic dystrophy type 1; DMD = Duchenne muscular dystrophy.

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Aiming to Deliver Functional Improvement for People Living with Neuromuscular Diseases Two clinical programs in registrational cohorts for DM1 and DMD following positive proof-of-concept data NEAR-TERM VALUE DRIVERS STRONG FINANCIAL POSITION LATE-STAGE PIPELINE Key data readouts in 2025 & 2026 potentially enabling two submissions for U.S. Accelerated Approval in 2026 Cash position of $677.5 million (as of 3/31/25) with expected runway into Q4 2026; all assets fully owned DM1 = myotonic dystrophy type 1; DMD = Duchenne muscular dystrophy; FSHD = facioscapulohumeral muscular dystrophy. FORCE DIFFERENTIATED PLATFORM FORCETM platform enables targeted delivery to muscle and CNS; broader pipeline includes FSHD and Pompe

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Q&A

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Appendix

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Consistent Splicing Correction Maintained Through Month 11 Splicing Improvement Median of multiple aliquots (revised approach) Single aliquot (original approach) New Data Note: One post-baseline sample in 3.4 mg/kg Q4W and one baseline sample in 6.8 mg/kg treatment groups not included within splicing assay as the sample did not meet QC criteria; Percent values in bars represent percent mean change, calculated as mean change from baseline divided by baseline mean; Single aliquot approach takes valid result from aliquot of highest quality based on visual inspection of tissue samples; In multiple aliquot approach, all aliquots are tested and median taken across those with valid results, up to 4. CASI-22 = composite alternative splicing index; SEM = standard error of the mean; 3 months = 85 days; 6 months = 169 days; 11 months = 309 days. \* Data confounded by missing baseline data and intra-patient sample variability. CASI-22 Change from Baseline +/- SEM -0.3 -0.2 -0.1 0 0.1 0.2 -0.3 -0.2 -0.1 0 0.1 0.2 n=14 n=5 n=6 n=5 n=14 n=6 n=6 n=5 n=6 n=6 n=5 3 months 6 months 11 months n=14 n=5 n=6 n=5 n=14 n=6 n=6 n=5 n=6 n=6 n=5 3 months 6 months 11 months CASI-22 Change from Baseline +/- SEM Placebo 3.4 mg/kg Q4W 5.4 mg/kg Q8W 6.8 mg/kg Q8W \*

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ACHIEVE Baseline Participant Characteristics: By Treatment Mean (SD) Placebo (N=14) 1.8 mg/kg Q4W (N=6) 3.4 mg/kg Q4W (N=6) 5.4 mg/kg Q8W (N=6) 6.8 mg/kg Q8W (N=6) Age (years) 32.6 (9.6) 37.0 (10.5) 31.2 (4.4) 40.2 (6.5) 37.2 (9.7) BMI (kg/m2) 24.4 (4.7) 21.6 (5.8) 21.1 (1.8) 21.4 (2.5) 23.4 (5.6) CASI-22 0.68 (0.20) 0.64 (0.25) 0.75 (0.12) 0.82 (0.16) 0.74 (0.25) CTG Repeats 597 (246) 303 (163) 652 (258) 482 (236) 542 (191) vHOT (sec) (middle finger) 7.5 (3.0) 11.3 (4.4) 6.6 (3.9) 11.9 (5.7) 7.8 (3.8) QMT Total (% predicted) 51.5 (14.3) 48.1 (10.6) 42.0 (12.6) 46.6 (17.7) 51.3 (10.4) 10MWR (sec) 3.34 (0.48) 3.39 (0.55) 3.48 (0.67) 5.1 (2.40) 3.94 (1.56) 5 Times Sit to Stand (sec) 9.24 (2.03) 9.47 (2.04) 8.75 (1.88) 12.78 (6.79) 9.98 (3.33) DM1-ACTIVc Total 47 (3.82) 46 (4.59) 38 (4.65) 44 (6.99) 43.4 (5.23) MDHI Total 18.7 (13.8) 23.5 (23.2) 30.2 (23.2) 14.8 (7.4) 26.5 (13.7)