Atamyo Therapeutics, a biotechnology company specializing in the development of next-generation gene therapies for limb-girdle muscular dystrophy (LGMD), announced at the MDA (Muscular Dystrophy Association) Conference 2026 the first safety, pharmacodynamics, and efficacy results for its ATA-200 gene therapy in LGMD-2C/R5 limb-girdle muscular dystrophy associated with γ-sarcoglycan deficiency (SGCG, gamma-sarcoglycanopathy). The results are from the first patients treated in the clinical trial conducted at the Powell Gene Therapy Center at the University of Florida by Dr. Barry Byrne and supported by The Dion Foundation for Children with Rare Diseases.

LGMD-2C/R5 is a severe form of muscular dystrophy that appears in childhood and causes loss of walking ability before adulthood, respiratory and heart failure, and premature death. This Phase 1b/2 clinical trial (NCT05973630) is a single-center study evaluating the safety, pharmacodynamics, efficacy, and immunogenicity of ATA-200 in children aged 6 to 13 years. ATA-200 is an adeno-associated virus (AAV) gene therapy carrying a normal copy of the human SGCGgene and administered as a single intravenous injection at a dose of 1.0E+14 vg/kg. This gene therapy product was developed by Isabelle Richard, a pioneer in the study of limb-girdle muscular dystrophies and the development of innovative therapies at Genethon.

At a dose of 1.0E+14 vg/kg, the following was observed in the first two patients treated with ATA-200:

• More than 90% of muscle fibers expressing the SGCG protein—demonstrating that almost all muscle fibers had received the therapeutic gene (90.2% for patient 1 and 92.1% for patient 2, biopsies at 6 months).

• A significant and sustained reduction in CPK levels (a biomarker of muscle damage) and a decrease in transaminases 9 months after treatment, demonstrating the significant efficacy of ATA-200 gene therapy.

• Also 9 months post-treatment, clinical benefits were observed on several other important parameters in ambulatory patients, particularly in timed functional tests.

No serious side effects were observed in the four patients treated, confirming the safety of the product.

"These initial results are very encouraging and demonstrate the potential of our product with biological data rarely seen in neuromuscular diseases and at such an early stage of the trial. I would like to commend the quality of the work done by the teams at Atamyo Therapeutics and, in particular, the commitment and determination of Isabelle Richard, which has made it possible to offer this hope to patients and their families. We are deeply grateful for the collaboration with the Dion Foundation and Dr. Barry Byrne of the Powell Gene Therapy Center and proud to offer children with LGMD-R5 the opportunity to receive a treatment that could change their lives." — Angela Columbano, CEO, Atamyo Therapeutics.

Further results from this ongoing study are expected to be published in the coming months, when new longer-term follow-up data becomes available.

We are grateful to the Dion Foundation for Children with Rare Diseases and CureSCG for their financial contributions that made it possible to launch the trial.