Solid Biosciences Reports Third Quarter 2025 Financial Results and Provides Update on INSPIRE DUCHENNE Clinical Trial Progress and Planned Regulatory Discussions - Duchenne (SGT-003): 23 participants have been dosed in t

Solid Biosciences Reports Third Quarter 2025 Financial Results and Provides Update on INSPIRE DUCHENNE

Clinical Trial Progress and Planned Regulatory Discussions

(SGT-003): 23 participants have been dosed in the INSPIRE DUCHENNE trial as of October 31, 2025; Solid expects to have dosed 30 participants in total by early 2026, then plans to meet with the

FDA to discuss potential registrational pathways in H1 2026 -

- SGT-003 has been generally

well tolerated using a steroid-only prophylactic immunomodulation regimen; cardiac safety monitoring continued to show reduction in cardiac injury and early signals of cardiac function normalization -

- Day 90 biopsy data from 10 treated participants (ages 5-10) showed all participants responded to

treatment with mean microdystrophin expression of 58% by western blot, 58% by mass spectrometry, mean microdystrophin positive fibers of 51% by immunofluorescence, and mean beta-sarcoglycan positive fibers of 50% by immunofluorescence -

- Strong statistical correlations observed between Day 90 microdystrophin expression levels and key components of the dystrophin-associated

protein complex (DAPC), beta-sarcoglycan (r = 0.95) and nNOS (r = 0.95), demonstrated evidence of SGT-003-mediated DAPC restoration and concordant signals of muscle

protection via reductions in CK levels (r = -0.78) -

- Solid has activated the first

clinical trial site and is currently screening participants for IMPACT DUCHENNE, a Phase 3 randomized, double-blind, placebo-controlled ex-U.S. clinical trial of SGT-003

- FA (SGT-212): Solid has activated the first clinical trial site

and is currently screening participants for FALCON, a Phase 1b first-in-human clinical trial evaluating SGT-212 for the treatment

of Friedreich's ataxia -

- CPVT (SGT-501): Clinical trial site

activation for ARTEMIS, a Phase 1b first-in-human clinical trial evaluating SGT-501 for the treatment of catecholaminergic

polymorphic ventricular tachycardia expected in Q4 2025 -

- Capsids (AAV-SLB101):

Over 30 agreements including licenses executed with corporations, institutions, and academic labs for the use of AAV-SLB101 -

- Cash: Company ended Q3 2025 with $236.1 million in cash, cash equivalents and available-for-sale securities; Solid has anticipated cash runway into H1 2027 -

CHARLESTOWN, MA, November 3, 2025 - Solid Biosciences Inc. (Nasdaq: SLDB) (the

"Company" or "Solid"), a life sciences company developing precision genetic medicines for neuromuscular and cardiac diseases, today reported financial results for the third quarter ended September 30, 2025, and announced

positive new interim data from the Phase 1/2 INSPIRE DUCHENNE clinical trial. The Company also provided an update to the planned timing of its meeting with the U.S. Food and Drug Administration (FDA) to discuss potential registrational pathways,

including accelerated approval pathways, for SGT-003.

Bo Cumbo, President and CEO of Solid Biosciences commented,

"The interim INSPIRE DUCHENNE data reported today strengthens our confidence in SGT-003's therapeutic potential. From strong observed biological correlations of

SGT-003 microdystrophin expression levels with properly localized restoration of key components of the dystrophin-associated protein complex to early evidence of cardiac function normalization, we are

observing a clear and cascading effect in the human body, suggesting a coordinated, systemic response to treatment. We believe these interim data represent one of the most thorough early analyses of any Duchenne gene therapy to date. The quality and

concurrence of these interim findings reinforce our conviction in SGT-003's potential to translate molecular impact into meaningful clinical outcomes."

Gabriel Brooks, MD, Chief Medical Officer of Solid Biosciences commented, "We are gratified and encouraged by the interim data observed to date. SGT-003 has been generally well tolerated with a minimally burdensome, prophylactic immunomodulatory regimen consisting of steroids alone. Importantly, early data suggests stabilization and improvement in cardiac

function, as evidenced by both reductions in elevated baseline serum cardiac troponin I levels and a normalization in left ventricular ejection fraction (LVEF). We look forward to monitoring these cardiac markers closely as potential key

differentiators of SGT-003."

Mr. Cumbo continued, "In light of the evolving regulatory landscape

and the rapid pace of enrollment in INSPIRE DUCHENNE, we have made the proactive decision to move our planned meeting with the FDA to the first half of 2026. The additional time will enable us to 1) generate a more fulsome data set for discussion

with the FDA, 2) work towards a comprehensive external comparator based on high-quality, well-matched natural history data, 3) begin our process performance qualification (PPQ) manufacturing runs with our CDMO partner in preparation for a potential

biologics license application (BLA) submission, and 4) initiate dosing in IMPACT DUCHENNE, our Phase 3 randomized, double-blind, placebo-controlled clinical trial that will be conducted outside of the United States. We believe these activities put

Solid in the best position to deliver the most compelling package to regulators.

"Our priority now is to rapidly build a robust data set to support

a potential accelerated regulatory pathway for SGT-003, and we are committed to executing with urgency to deliver on SGT-003's potential as quickly as possible.

Beyond SGT-003, our lead pipeline programs continue to progress. We are excited to announce that we have recently activated the first clinical trial site for FALCON, a first-in-human Phase 1b clinical trial evaluating our novel dual route Friedreich's ataxia gene therapy candidate, SGT-212. Later in the fourth quarter of 2025,

we also expect to activate our first clinical trial site for ARTEMIS, a first-in-human Phase 1b clinical trial evaluating

SGT-501, our gene therapy candidate intended to treat catecholaminergic polymorphic ventricular tachycardia. We look forward to continued advancement across our suite of therapeutics and delivery technologies

in the quarters to come," Mr. Cumbo concluded.

INSPIRE DUCHENNE - Interim Clinical Data Update

INSPIRE DUCHENNE is a Phase 1/2 first-in-human, open-label, single-dose,

multicenter trial designed to evaluate the safety, tolerability and efficacy of SGT-003 in pediatric participants with Duchenne at a dose level of 1E14vg/kg. SGT-003 is

administered as a one-time intravenous infusion.

The interim clinical data reported in this release are as of a

September 29, 2025, data cutoff date, with additional safety data reported as of October 31, 2025. As of October 31, 2025, 23 participants have been dosed in the trial. Enrollment in INSPIRE DUCHENNE is ongoing at 15 clinical trial

sites across the United States, Canada, Italy and the United Kingdom. The Company expects to dose a total of 30 participants by early 2026.

correlations, as measured by the Pearson correlation coefficient, were observed between Day 90 SGT-003 microdystrophin therapy and reconstitution of key components of the dystrophin-associated protein complex

(DAPC), including beta-sarcoglycan and neuronal nitric oxide synthase (nNOS). Beta-sarcoglycan is a critical component of the dystrophin associated / sarcoglycan complex that is highly expressed in cardiac and skeletal muscle and plays a crucial

role in maintaining muscle integrity. Myopathy and cardiomyopathy are observed in diseases in which the sarcoglycan complex is absent. nNOS plays an important role in protecting cardiac and skeletal muscle by improving vasodilation and reducing

functional ischemia and muscle breakdown. Solid's microdystrophin construct is the only microdystrophin gene therapy, approved or investigational, that contains the R16/R17 binding domain, which localizes nNOS to the muscle membrane.

Strong correlations were also observed between SGT-003 microdystrophin therapy and improvements in several biomarkers

of muscle integrity, including serum creatine kinase (CK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST) and embryonic myosin heavy chain (eMHC), suggesting a coordinated downstream effect of treatment with SGT-003.

SGT-003, utilizing the

Company's proprietary, rationally designed capsid, AAV-SLB101, has demonstrated strong transduction, achieving a mean of 13 vector copies per nucleus (N=10) at Day 90, along with meaningful restoration

of biologic correlates across several measures of microdystrophin, components of the DAPC, and multiple biomarkers of muscle integrity and preservation.

In the 10 participants (aged 5-10) whose Day 90 biopsies were evaluated as of the September 29, 2025, data cutoff

date, the Company observed mean microdystrophin expression of 58%, as measured by both western blot and mass spectrometry, and mean microdystrophin positive fibers of 51%, as measured by immunofluorescence. Furthermore, in each of those 10

participants, the Company observed properly localized and restored beta-sarcoglycan positive fibers at the mean 50% level as measured by immunofluorescence and nNOS activity-positive fibers (a less sensitive activity assay) at the mean 26% level.

Available Day 360 biopsy data from 2 participants (aged 5) as of September 29, 2025, demonstrated encouraging and durable transduction, achieving a

mean of 12 vector copies per nucleus, as well as robust mean microdystrophin expression of 107%, as measured by western blot, and 100%, as measured by mass spectrometry, mean microdystrophin positive fibers of 67% and mean beta-sarcoglycan positive

fibers of 70%, both measured by immunofluorescence, and mean nNOS activity-positive fibers of 36%.

Additionally, a mean 49% reduction in percent eMHC positive fibers, a histologic marker of muscle

regeneration and disease progression, was observed at Day 90 (N=10). As muscle fibers deteriorate, muscle stem cells are activated to repair and replace damaged muscle fibers; during this process, new muscle fibers transiently express eMHC. In

Duchenne, this stem cell-mediated repair process is futile because muscle fibers that are developed from stem cells lack dystrophin and therefore will be dystrophic. Consequently, the presence of eMHC positive fibers is an informative biomarker of

disease progression, signaling constant muscle injury, breakdown and deterioration. A treatment-mediated decrease in eMHC is a favorable observation, and in combination with other markers of reduced muscle injury, suggests overall muscle

Favorable reductions across a range of biomarkers of muscle injury and breakdown were observed through both Day 90 and Day 360:

INSPIRE DUCHENNE - Interim Cardiac Monitoring

Cardiomyopathy is a leading cause of death in Duchenne, with 25% of individuals displaying evidence of cardiomyopathy by six years of age, increasing to 59% by

Mean cardiac function trended into normal LVEF ranges (60-69%)2 for all SGT-003-treated participants who reached the Day 180 follow-up timepoint (N=8) as of the September 29, 2025, data cutoff date. Though cardiac injury biomarkers and cardiac imaging were collected primarily for safety analysis, early data may indicate a potential

for benefit through reduction in troponin I (cTnI) and increased systolic function as measured by LVEF by echocardiography. Observed increases in systolic function as measured by LVEF appeared to have been driven largely by participants with low to low-normal systolic function at baseline.

Mean reductions from baseline in serum cTnI of 31% at Day 90 (N=14) and 70%

at Day 360 (N=3) were observed with reductions driven by participants who entered the trial with elevated baseline cTnI levels. cTnI is an important marker that can be predictive of severe cardiac disease in neuromuscular diagnoses.

INSPIRE DUCHENNE - Interim Safety Update

SGT-003 has been generally well tolerated in the 23 participants dosed as of October 31, 2025. Steroids alone were

utilized as the prophylactic immunomodulation regimen. Signals of asymptomatic and self-resolving platelet declines and thrombocytopenia observed in early participants in the trial have been ameliorated in subsequent participants.

As of October 31, 2025, there was one treatment-related serious adverse event (SAE) reported in the

INSPIRE DUCHENNE trial. This SAE was identified as a Grade 3 immune-mediated myositis which, importantly, was not associated with muscle pain or weakness, and occurred in a participant who had a large deletion in a region coded for by SGT-003's microdystrophin. The participant promptly responded to steroid treatment with all clinical symptoms noted at presentation resolving and with muscle biomarkers, including CK, declining

well below baseline levels. This SAE was reviewed by the trial data and safety monitoring board (DSMB) with the recommendation to continue dosing without interruption.

In Duchenne muscular dystrophy, transaminase elevations are the result of ongoing muscle injury as opposed to liver injury. Therapeutic interventions that

lead to reductions in transaminases therefore indicate muscle protection in the setting of an avoidance of demonstrable liver injury, especially when more specific liver injury markers remain stable. As of the September 29, 2025, data cutoff date,

we observed a mean alanine transaminase (ALT) reduction of 41% (N=14), a mean aspartate transaminase (AST) reduction of 25% (N=14) and stable mean gamma-glutamyl transferase (GGT) levels through Day 90 (N=14). Mean reductions of 40% AST and 29% ALT

were observed in the three participants who reached the Day 360 follow-up.

There have been no cases of

drug-induced liver injury (DILI) observed as of October 31, 2025 (N=23).

A presentation summarizing the interim data update can be accessed on the

Presentations page of the Investors section of the Company's website.

SGT-003 Regulatory Update

Solid plans to meet with the FDA in the first half of 2026 to discuss potential registrational pathways, including accelerated approval pathways, for SGT-003. Solid continues to dose participants in the INSPIRE DUCHENNE trial in the interim, with additional participant safety, clinical activity and functional data expected to enable a more robust discussion with

Critically, Solid has aligned with the FDA on SGT-003's potency assay strategy and will continue

additional commercial-readiness CMC activities, with PPQ manufacturing batches expected to be completed in 2026.

In October 2025, Solid activated the