Abstract Dilated cardiomyopathy (DCM) is the second most common cause for heart failure with no cure except a high-risk heart transplantation. Approximately 30% of DCM patients harbor heritable mutations which are amenable to CRISPR-based gene therapy 1 . However, challenges related to delivery of the editing complex and off-target concerns hamper the broad applicability of CRISPR agents in the heart 2 . We employed a combination of the viral gene transfer vector AAVMYO with superior targeting specificity of heart muscle tissue 3 and CRISPR base editors to repair patient mutations in the cardiac splice factor Rbm20 , which cause aggressive and arrhythmogenic DCM 4 . Using optimized conditions, we could improve splice defects in human iPSC-derived cardiomyocytes (iPSC-CMs) and repair &gt;70% of cardiomyocytes in two Rbm20 knock-in mouse models that we generated to serve as an in vivo platform of our editing strategy. Treatment of juvenile mice restored the localization defect of RBM20 in 75% of cells and splicing of RBM20 targets including TTN. Three months after injection, cardiac dilation and ejection fraction reached wildtype levels. Single-nuclei RNA sequencing (snRNA-seq) uncovered restoration of the transcriptional profile across all major cardiac cell types and whole-genome sequencing (WGS) revealed no evidence for aberrant off-target editing. Our study highlights the potential of base editors combined with AAVMYO to achieve gene repair for treatment of hereditary cardiac diseases.

Striated muscle-specific base editing enables correction of mutations causing dilated cardiomyopathy