Exon-skipping

A therapeutic approach to treat genetic disorders by modifying RNA splicing

Exon-skipping is a molecular technique used to modify the splicing of pre-mRNA in order to skip over faulty or mutated exons during the process of RNA splicing. This approach is primarily used as a therapeutic strategy to treat certain genetic disorders, such as Duchenne muscular dystrophy (DMD), by restoring the reading frame of the mRNA and allowing for the production of a functional protein, albeit shorter than the wild-type.

Mechanism of Exon-Skipping

Exon-skipping involves the use of synthetic molecules called antisense oligonucleotides (AONs) that bind to specific sequences in the pre-mRNA. These AONs are designed to mask the splice sites of the targeted exon, preventing the spliceosome from recognizing and including it in the mature mRNA. As a result, the exon is "skipped" during splicing, and the remaining exons are joined together, potentially restoring the open reading frame of the mRNA.

Antisense Oligonucleotides

Antisense oligonucleotides are short, synthetic strands of nucleic acids that are complementary to the target RNA sequence. They can be chemically modified to enhance their stability, binding affinity, and resistance to degradation by nucleases. Common modifications include the use of phosphorothioate backbones and 2'-O-methyl or 2'-O-methoxyethyl modifications.

Applications in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is a severe X-linked recessive disorder caused by mutations in the dystrophin gene, leading to the absence of functional dystrophin protein. Exon-skipping aims to convert a DMD phenotype into a milder Becker muscular dystrophy phenotype by skipping exons that contain mutations, thereby restoring the reading frame and allowing for the production of a truncated but partially functional dystrophin protein.

Clinical Trials and Approvals

Several exon-skipping drugs have been developed and tested in clinical trials. Notably, eteplirsen (Exondys 51) was the first exon-skipping drug approved by the U.S. Food and Drug Administration (FDA) for the treatment of DMD in patients amenable to exon 51 skipping. Other drugs targeting different exons, such as golodirsen and viltolarsen, have also received approval or are undergoing clinical evaluation.

Challenges and Future Directions

While exon-skipping holds promise, there are several challenges that need to be addressed:

• Delivery: Efficient delivery of AONs to target tissues, especially muscle tissue, remains a significant hurdle.
• Efficacy: The level of dystrophin restoration achieved by exon-skipping is often partial, and the clinical benefits can vary among patients.
• Safety: Long-term safety and potential off-target effects of AONs need to be thoroughly evaluated.

Future research is focused on improving the delivery methods, enhancing the potency of AONs, and expanding the applicability of exon-skipping to other genetic disorders.

Also see

• RNA splicing
• Antisense therapy
• Gene therapy
• Duchenne muscular dystrophy
• Becker muscular dystrophy