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Updated: Nov 8, 2025
Characterizing Exon Skipping Efficiency in DMD Patient Samples in Clinical Trials of Antisense Oligonucleotides
Published on: May 7, 2020
Pre-clinical dose-escalation studies establish a therapeutic range for U7snRNA-mediated DMD exon 2 skipping
Tabatha R Simmons1, Tatyana A Vetter1, Nianyuan Huang1
1Center for Gene Therapy, Abigail Wexner Research Institute, Nationwide Children's Hospital, Columbus, OH 43205, USA.
Abstract:
Duchenne muscular dystrophy (DMD) is an X-linked progressive disease characterized by loss of dystrophin protein that typically results from truncating mutations in the DMD gene. Current exon-skipping therapies have sought to treat deletion mutations that abolish an open reading frame (ORF) by skipping an adjacent exon, in order to restore an ORF that allows translation of an internally deleted yet partially functional protein, as is seen with many patients with the milder Becker muscular dystrophy (BMD) phenotype. In contrast to that approach, skipping of one copy of a duplicated exon would be expected to result in a full-length transcript and production of a wild-type protein. We have developed an adeno-associated virus (AAV)-based U7snRNA exon-skipping approach directed toward exon 2, duplications of which represent 10% of all DMD duplication mutations. Deletion of exon 2 results in utilization of an exon 5 internal ribosome entry site (IRES) that allows translation beginning in exon 6 of a highly protective dystrophin protein, providing a wide therapeutic window for treatment. Both intramuscular and systemic administration of this vector in the Dup2 mouse model results in robust dystrophin expression and correction of muscle physiologic defects, allowing dose escalation to establish a putative minimal efficacious dose for a human clinical trial.
Insights
This study developed an AAV-based exon-skipping therapy for Duchenne muscular dystrophy (DMD) duplications. The approach successfully restored dystrophin protein expression and corrected muscle defects in a mouse model.
Area of Science:
- Genetics
- Molecular Biology
- Neurology
Background:
- Duchenne muscular dystrophy (DMD) is a severe X-linked genetic disorder caused by mutations in the DMD gene, leading to dystrophin deficiency.
- Current exon-skipping therapies aim to restore dystrophin by bypassing mutated exons in deletion mutations.
- Duplication mutations in the DMD gene, specifically exon 2 duplications, account for 10% of DMD cases and require different therapeutic strategies.
Purpose of the Study:
- To develop and evaluate an adeno-associated virus (AAV)-based U7snRNA exon-skipping strategy targeting exon 2 duplications in the DMD gene.
- To assess the efficacy of this therapeutic approach in restoring functional dystrophin protein and correcting muscle defects in a relevant animal model.
Main Methods:
- Development of an AAV vector encoding U7snRNA designed to skip exon 2 of the DMD gene.
- Administration of the AAV vector via intramuscular and systemic routes in the Dup2 mouse model of DMD duplications.
- Assessment of dystrophin expression, muscle physiology, and therapeutic efficacy following treatment.
Main Results:
- The AAV-U7snRNA approach successfully induced skipping of exon 2, leading to the production of a functional dystrophin protein.
- Both intramuscular and systemic delivery resulted in robust dystrophin expression in the Dup2 mouse model.
- Significant correction of muscle physiologic defects was observed, demonstrating the therapeutic potential of the approach.
Conclusions:
- Exon-skipping targeting exon 2 duplications is a viable therapeutic strategy for DMD.
- AAV-mediated delivery of U7snRNA shows promise for treating DMD duplications.
- The study provides a foundation for establishing a minimal efficacious dose for future human clinical trials.
