Letter to the Duchenne Community – INSPIRE DUCHENNE update & expansion

Dear Duchenne Community,

Earlier today we reported third quarter financial results and provided updates on Solid Biociences Inc.’ (“Solid”) business. Among the highlights, we shared new information about INSPIRE DUCHENNE, our clinical trial of our next-generation AAV gene therapy candidate, SGT-003, for the treatment of patients living with Duchenne.

Status update

INSPIRE DUCHENNE is a first-in-human, multicenter, Phase 1/2 open-label study investigating the safety, tolerability, and efficacy of a single IV infusion of SGT-003 in ambulant boys with Duchenne. We are pleased to share that three participants have been dosed in the study and SGT-003 has been well tolerated to date with no serious adverse events reported. We plan to share safety, expression and biomarker data from the first three patients, along with a trial update, in the first quarter of 2025.

Clinical Study Expansion

Given the encouraging early results seen in the study thus far, we have expanded the target enrollment to 43 participants and broadened the age range for participation from the previous 4 to <8 years to 4 to <12 years. Additionally, we have modified the timepoint for evaluation of functional endpoints from 12 months to 18 months to better detect the ability of SGT-003 to impact the course of disease.

To support the study expansion, we have activated one additional site and plan to add three new clinical sites across the U.S. and Canada before the end of the year. Actively enrolling INSPIRE DUCHENNE sites include:

• Nationwide Children’s Hospital, Columbus, OH

• University of California Los Angeles Medical Center, Los Angeles, CA

• University of California Davis Medical Center, Sacramento, CA

Upcoming INSPIRE DUCHENNE sites include:

• Arkansas Children’s Hospital, Little Rock, AR

• Children’s Hospital of the King’s Daughters, Norfolk, VA

• The Hospital for Sick Children (SickKids), Toronto, Canada

We are also planning to expand the study into Europe during the first half of 2025, which we hope will allow more families the opportunity to participate in the study and contribute to the advancement of this new, potential treatment option.

For more study information, including eligibility criteria and clinical site contacts please visit: https://clinicaltrials.gov/ct2/show/NCT06138639

Engaging with the Duchenne patient community has always been a cornerstone of Solid’s mission and is critical to our progress. To that end, we are partnering with three advocacy organizations to host community webinars in the coming weeks. During the webinars, members of Solid’s Clinical and Patient Advocacy teams will share more information about INSPIRE DUCHENNE.

Parent Project Muscular Dystrophy Community Webinar Tuesday, November 12, 2024, 1 p.m. EST Registration

Defeat Duchenne Canada Community Webinar Wednesday, November 13, 2024, 1 p.m. EST Registration

Jett Foundation Community Webinar Thursday, November 21, 2024, 1 p.m. EST Registration

We are deeply grateful to patients and families who choose to participate in clinical trials and contribute in such meaningful ways to scientific research. We also sincerely appreciate the partnership of our clinical site teams for their efforts in support of patients and families and their commitment to the discovery and development of new potential treatments for Duchenne.

The Solid team remains infinitely committed to the Duchenne community and to our purpose of improving the lives of patients living with Duchenne and other rare neuromuscular and cardiac conditions.

#TogetherWeAreSolid

Sincerely, Annie Ganot Vice President, Patient Advocacy