Engineered CRISPR-Base Editors as a Permanent Treatment for Familial Dysautonomia.

Familial dysautonomia (FD) is a fatal autosomal recessive congenital neuropathy caused by a T-to-C mutation in intron 20 of the () gene, which causes tissue-specific skipping of exon 20 and reduction of ELP1 protein. Here, we developed a base editor (BE) approach to precisely correct this mutation. By optimizing Cas9 variants and screening multiple gRNAs, we identified a combination that was able to promote up to 70% on-target editing in HEK293T cells harboring the T-to-C mutation. These editing levels were sufficient to restore exon 20 inclusion in the transcript. Moreover, we optimized an engineered dual intein-split system to deliver these constructs . Mediated by adeno-associated virus (AAV) delivery, this BE strategy effectively corrected the liver and brain splicing defects in a humanized FD mouse model carrying the T-to-C mutation and rescued the FD phenotype in iPSC-derived sympathetic neurons. Importantly, we observed minimal off-target editing demonstrating high levels of specificity with these optimized base editors. These findings establish a novel and highly precise BE-based therapeutic approach to correct the FD mutation and associated splicing defects and provide the foundation for the development of a transformative, permanent treatment for this devastating disease.