David Argyelan

Background: Duchenne Muscular Dystrophy (DMD) is a fatal X-linked muscle wasting disease affecting approximately 0.02% of male newborns. Characterized by progressive muscle weakness and degeneration starting in early life, DMD arises from mutations in the dystrophin gene, leading to a dysfunctional or absent dystrophin protein essential for muscle fiber stability. In its absence, muscle contractions cause repeated damage, ultimately leading to muscle degeneration and fibrosis. Currently, there is no cure for DMD, with available interventions focusing on symptom management and slowing disease progression^1,2. Patients suffering from DMD have a life expectancy of less than 30 years, with a low quality of life in the later years¹. However, recent advancements in genetic manipulation offer promising avenues for therapeutic development^3,4,5.

Objective: This review explores the potential of exon skipping using antisense oligonucleotides (ASOs) as a therapeutic approach for Duchenne Muscular Dystrophy.

Search Methods: A comprehensive literature search was conducted using the PubMed database, focusing on primary research articles published between 2018 and 2024. Search terms included “Duchenne Muscular Dystrophy,” “antisense oligonucleotides,” “DMD gene editing,” and “Exon skipping Duchenne Muscular Dystrophy.”

Results: Two main strategies for exon skipping were identified: base and prime editing, and antisense oligonucleotides (ASOs). Base and prime editing utilizes the Cas9 enzyme to modify DNA bases within splice motifs, inducing the skipping of specific exons in the dystrophin gene. Studies in mouse models have demonstrated successful exon skipping and restoration of dystrophin protein, leading to improved muscle function³. ASOs are small synthetic DNA or RNA molecules designed to bind to specific mRNA regions, disrupting the splicing process and triggering the “skipping” of targeted exons. Recent advancements in ASO technology have addressed limitations of earlier approaches. Multi-exon skipping utilizes multiple ASOs delivered simultaneously to achieve skipping of not only exon 51 (applicable to approximately 13% of DMD patients) but also exons 45-55, potentially broadening applicability to up to 50% of patients. This approach results in a highly stable, truncated protein similar to that found in individuals with Becker Muscular Dystrophy (BMD), a milder form of the disease⁴. Furthermore, targeting multiple exon sites within exon 51 has emerged as another strategy to enhance the efficiency of exon-51 skipping ASOs. By targeting two distinct sites simultaneously, exon skipping efficiency can be increased 65-fold compared to Drisapersen, an ASO previously used in clinical trials. This approach led to up to 40% dystrophin restoration and normalization of serum biomarkers in a mouse model, suggesting improved muscle membrane integrity⁵.

Conclusion: Exon skipping using ASOs holds immense promise as a potential therapeutic approach for Duchenne Muscular Dystrophy. The ability to target multiple exons and optimize skipping efficiency through various modifications opens doors to broader applicability and potentially greater therapeutic benefit for a larger population of DMD patients. Further research and clinical trials are crucial to translate these promising findings into effective therapies. Future studies should prioritize evaluating the safety and efficacy of these ASOs in the more relevant canine model of DMD¹, which more closely mimics human disease progression.

Works Cited:

1. Hildyard JCW, Riddell DO, Harron RCM, et al. The skeletal muscle phenotype of the DE50-MD dog model of Duchenne muscular dystrophy. Wellcome Open Res. 2022;7:238. doi:10.12688/wellcomeopenres.18251.1
2. Yamauchi N, Tamai K, Kimura I, et al. High-intensity interval training in the form of isometric contraction improves fatigue resistance in dystrophin-deficient muscle. The Journal of Physiology. 2023;601(14):2917-2933. doi:10.1113/JP284532
3. Chemello F, Chai AC, Li H, et al. Precise correction of Duchenne muscular dystrophy exon deletion mutations by base and prime editing. Sci Adv. 2021;7(18):eabg4910. doi:10.1126/sciadv.abg4910
4. Lee J, Echigoya Y, Duddy W, et al. Antisense PMO cocktails effectively skip dystrophin exons 45-55 in myotubes transdifferentiated from DMD patient fibroblasts. PLOS ONE. 2018;13(5):e0197084. doi:10.1371/journal.pone.0197084
5. van Deutekom J, Beekman C, Bijl S, et al. Next Generation Exon 51 Skipping Antisense Oligonucleotides for Duchenne Muscular Dystrophy. Nucleic Acid Ther. 2023;33(3):193-208. doi:10.1089/nat.2022.0063