- Initiation of Phase 3 IMPACT DUCHENNE placebo-controlled, randomized, double-blind trial as part of Solid’s integrated, multi-trial development program designed to support registration and global regulatory authorizations for SGT-003 -

- Solid received a positive opinion from the European Medicines Agency (EMA) on its Pediatric Investigation Plan (PIP) for SGT-003, establishing alignment on a pediatric clinical development framework in Europe -

- 46 participants have been dosed with SGT-003 in the Phase 1/2 INSPIRE DUCHENNE clinical trial using a steroid-only prophylactic immunomodulation regimen; SGT-003 has been generally well tolerated as of a May 4, 2026, cutoff date -

 Solid Biosciences Inc. (Nasdaq: SLDB) (the “Company” or “Solid”), a life sciences company developing precision genetic medicines for neuromuscular and cardiac diseases, announced that the first participant has been dosed in IMPACT DUCHENNE, the Company’s multi-country, placebo-controlled, randomized, double-blind, Phase 3 clinical trial investigating SGT-003 for the treatment of Duchenne muscular dystrophy (Duchenne).

IMPACT DUCHENNE and the ongoing Phase 1/2 INSPIRE DUCHENNE clinical trials are components of an integrated, multi-trial clinical development program designed to evaluate the safety and efficacy of a single intravenous dose of SGT-003 in individuals living with Duchenne. Since the initiation of the INSPIRE DUCHENNE trial in June 2024, SGT-003 has been administered to 46 participants, with approximately 30 participants dosed as of year-end 2025. As of a May 4, 2026, safety cutoff, SGT-003, which is administered using a steroid-only prophylactic immunomodulation regimen, has been generally well tolerated with no observed cases of drug induced liver injury, myocarditis, thrombotic microangiopathy or atypical hemolytic uremic syndrome.

The initiation of the Phase 3 IMPACT DUCHENNE trial reflects Solid’s deliberate approach to generating well-controlled clinical data in a randomized and blinded setting to support potential accelerated approval and inform further regulatory interactions. The Company continues to engage with the US Food and Drug Administration (FDA) and is committed to ongoing collaboration with the Agency to address the unmet need in Duchenne.

“Dosing the first participant in our Phase 3 trial marks a critical moment for Solid Biosciences and for the Duchenne community,” said Gabriel Brooks, M.D., Chief Medical Officer of Solid Biosciences. “With the initiation of a randomized, placebo-controlled clinical trial, we are reinforcing our conviction in SGT-003 and our long-standing commitment to generating well-controlled, high-quality data. Families living with Duchenne continue to face difficult treatment decisions in a setting of significant unmet medical need. Solid remains focused on helping inform the Duchenne community of potential additional treatment options through the responsible and rigorous clinical evaluation of SGT-003.”

The first participant was dosed in Australia at The Children’s Hospital at Westmead.

Global Regulatory Updates
In the US, Solid previously announced the outcome of a Type C meeting with the FDA during which alignment was reached on the overall IMPACT DUCHENNE trial design, including the pre-specified primary endpoint of change from baseline at 18 months in time to rise from supine (TTR) velocity. The Phase 3 trial is designed to play a key role in supporting various US and ex-US regulatory pathways. Additionally, SGT-003 has received FDA Fast Track, Rare Pediatric and Orphan Drug designations.

Solid has also made significant progress in advancing the regulatory strategy for SGT-003 across the globe. The Company has received a positive opinion from the EMA’s Paediatric Committee on its Pediatric Investigation Plan (PIP), providing alignment on the proposed pediatric development framework for SGT-003 in Europe. Approval of a PIP is required for a future marketing authorization application. The finalization of the PIP, together with receipt of Orphan drug designation from the European Commission, reflect Solid’s progress in advancing SGT-003 in Europe.

In addition, Solid was one of only three recipients of the newly relaunched Innovation Passport under the UK’s Innovative Licensing and Access Pathway (ILAP), which focuses more selectively on transformative products that address unmet clinical needs. Solid has had multiple engagements under this designation with the goal of mapping an accelerated time to market as well as expedited patient access.