Letter to the Duchenne Community:

With heartfelt gratitude, I want to begin by thanking the patients and families participating in the INSPIRE DUCHENNE clinical study – you are the true heroes of this journey. Your bravery and commitment are what drive our work as we strive to advance a more effective and safe gene therapy treatment option for patients living with Duchenne.

A Great Start!

We are pleased to provide an update on our Phase 1/2 clinical study of SGT-003, our next generation gene therapy candidate for Duchenne. The initial 90-day data from the first three patients, two 5-year-old boys and one 7-year-old boy, offer valuable insights into how SGT-003 is behaving in the body, showing an average microdystrophin expression of 110% and improvements in multiple muscle health biomarkers. In addition to microdystrophin expression, we have observed reductions in key muscle injury markers – CK, AST, ALT, Titin, LDH and eMHC, suggesting potential stabilization of muscle health. We have also seen promising signs of muscle function preservation, further reinforcing our cautious optimism for the therapy’s potential impact. Additionally, we saw encouraging early findings in potential cardiac benefit. Though early, these signals strengthen our hope that SGT-003 may not only improve skeletal muscle but also positively impact heart health—something we know is critically important in Duchenne.

SGT-003 has been well-tolerated across the six patients dosed to date. The most common side effects observed were mild and typical of AAV-based gene therapies, including nausea, vomiting, fever, and temporary decreases in platelet levels. Importantly, no serious adverse events (SAEs) were observed. These findings provide early reassurance about the safety profile of SGT-003 as we continue to gather data.

What’s Next?

We are still in the early days of the INSPIRE DUCHENNE clinical study. We anticipate enrolling approximately 20 total patients by the end of 2025. We are actively enrolling patients at six clinical trial sites across the United States and Canada and have regulatory approvals to expand to the U.K. and Italy.

In mid-2025, we plan to request a meeting with the U.S. Food and Drug Administration (FDA) to discuss the potential for an accelerated approval pathway for SGT-003, a significant step toward bringing this therapy to the broader Duchenne community as quickly and safely as possible.

Join Us for More Updates

We invite you to tune in to our company conference call today, February 18 at 8:00 AM ET, where we will discuss these findings in more detail. The call may be accessed via the Events page of our website at Events • Solid Biosciences Inc.

Parent Project Muscular Dystrophy (PPMD) will host a community webinar with members of the Solid Biosciences team on Tuesday, February 25 at 1:00 PM ET. We welcome the opportunity to provide an update and take questions from the community. Webinar Registration – Zoom

Upcoming conferences:

Parent Project Italy 22nd Annual International Conference

February 28 – March 2, 2025

Rome, Italy

Duchenne UK New Horizons Conference

March 28 – 29, 2025

London, UK

Sincerely,

Annie Ganot

Co-founder & Head of Patient Advocacy

Solid Biosciences