Insights:Letter to the Duchenne Community

Dear Duchenne Community –

Since day one, Solid Biosciences has been focused on developing meaningful therapies for patients with Duchenne muscular dystrophy. This cause is deeply embedded in our organization, which was founded by individuals impacted by Duchenne.

Today, we are pleased to announce that Solid received clearance by the U.S. Food and Drug Administration (FDA) for an Investigational New Drug (IND) application for SGT-003, our next generation microdystrophin gene therapy candidate for the treatment of Duchenne.

SGT-003 combines our differentiated microdystrophin transgene with a new, novel capsid designed to substantially increase the amount of drug delivered to muscle compared to first generation capsids. In pre-clinical studies this has resulted in higher levels of microdystrophin expression and greater improvements in muscle function. In addition, SGT-003 is manufactured using an improved process to maintain a high level of full capsids and overall drug purity.

The IND clearance enables us to begin working with urgency to enroll patients in INSPIRE DUCHENNE, a Phase 1/2 multicenter clinical trial to primarily evaluate the safety and tolerability of SGT-003. The study will include two separate cohorts based on age, beginning with patients 4 and 5 years old. All participants will receive a one-time intravenous infusion of SGT-003 at a single dose level. Long-term safety and efficacy will be evaluated for a total of five years following treatment.

Working alongside the Duchenne patient community has always been an honor as well as critical to our progress. To that end, we will be scheduling a free community webinar, hosted by Parent Project Muscular Dystrophy, in the coming weeks. Details and registration information will be shared soon. During the webinar, members of the Solid team will share more information about the clinical study, including sites and eligibility criteria.

We are infinitely grateful to patients and families who choose to participate in clinical trials and contribute to ongoing research. We are excited to once again initiate a clinical trial and continue forging a path toward a safe and effective treatment for Duchenne. We look forward to keeping the community informed of progress with our INSPIRE DUCHENNE clinical program. The Solid team remains relentless and motivated to make a meaningful impact on the lives of patients living with Duchenne.



Your Solid Biosciences Team