Prime editing of the common Familial Dysautonomia-causing c.2204 + 6T > C splicing mutation.

Familial Dysautonomia (FD, OMIM #223900) is a rare, life-threatening autosomal recessive neuropathy caused in 99.8% of patients by the c.2204 + 6T > C intronic mutation in the ELP1/IKAP gene. This substitution induces exon 20 skipping, leading to reduced ELP1 expression. While splicing-modulating therapies have shown partial efficacy, a permanent genetic correction remains unavailable. Here, we report the first application of Prime Editing (PE) to rescue the FD-causing IKAP splicing defect. Using a mutant exon-trapping minigene (pTB-IKAP) transiently co-transfected in HEK293T cells with PE2 or PE3 components, we demonstrate a significant increase in exon 20 inclusion, from 19 ± 2% to 48 ± 3% and 60 ± 3%, respectively. Restriction fragment length polymorphism and Sanger sequencing confirmed correction of the mutant allele, with PE3 achieving ~ 10% genomic editing efficiency. Moreover, by targeting ESS2 via a silent A > G substitution, we similarly restored exon inclusion to 50 ± 4%. These findings provide proof-of-principle that prime editing, particularly PE3, can efficiently correct or bypass the ELP1/IKAP c.2204 + 6T > C mutation and restore proper splicing. Given that modest increases in ELP1 expression (5-10% of wild-type) markedly alleviate FD severity in mouse models, our results highlight PE as a promising, potentially curative approach and lay the foundation for future ex-vivo and in vivo studies.