Background

Duchenne muscular dystrophy (DMD) is a severe genetic disorder caused by mutations in the DMD gene. These mutations disrupt the dystrophin protein, essential for muscle function. Current treatments, such as exon-skipping oligonucleotides, have limitations due to their short lifespan and the need for frequent administration.

Objective

This study explored the use of a self-complementary adeno-associated virus (scAAV9) vector expressing U7 small nuclear RNA (snRNA) to target exon 2 of the DMD gene. This approach aims to restore dystrophin expression by inducing exon skipping.

Methods

The vector was tested in a Dup2 mouse model, which carries a duplication of exon 2. Two strategies were assessed:

• One-time systemic injection at neonatal or adult stages.
• Co-treatment with prednisolone.

Efficacy was evaluated using RT-PCR, Western blot, immunofluorescence, and histopathological assessments.

Findings (Adults)

Injection in 2-month-old mice resulted in:

• 69-95% exon skipping.
• Significant dystrophin restoration.
• Immunofluorescence showed 33-53% intensity and up to 79% positive fibers, improving muscle structure and function.

Findings (Neonates)

Neonatal injection achieved:

• Up to 99% dystrophin-positive fibers.
• Near-complete disease correction over six months.
• Persistent exon skipping and robust dystrophin production without significant off-target effects.

Conclusions

The results demonstrate that scAAV9.U7snRNA.ACCA provides durable, robust dystrophin restoration, supporting its potential as a clinical therapy for DMD, especially for exon 2 duplications.