RNA exon editing: Splicing the way to treat human diseases

RNA exon editing is a therapeutic strategy for correcting disease-causing mutations by inducing trans-splicing between a synthetic RNA molecule and an endogenous pre-mRNA target, resulting in functionally restored mRNA and protein. This approach enables the replacement of exons at the kilobase scale, addresses multiple mutations with a single therapy, and maintains native gene expression without changes to DNA. For genes larger than 5 kb, RNA exon editors can be delivered in a single vector despite AAV capacity limitations because only mutated exons need to be replaced. While correcting mutations by trans-splicing has been previously demonstrated, prior attempts were hampered by low efficiency or lack of translation in preclinical models. Advances in synthetic biology, next-generation sequencing, and bioinformatics, with a deeper understanding of mechanisms controlling RNA splicing, have triggered a re-emergence of trans-splicing and the development of new RNA exon editing molecules for treating human disease, including the first application in a clinical trial (this study was registered at ClinicalTrials.gov [NCT06467344]). Here, we provide an overview of RNA splicing, the history of trans-splicing, previously reported therapeutic applications, and how modern advances are enabling the discovery of RNA exon editing molecules for genetic targets unable to be addressed by conventional gene therapy and gene editing approaches.