Adenine base editing-mediated exon skipping restores dystrophin in humanized Duchenne mouse model

Duchenne muscular dystrophy (DMD) affecting 1 in 3500–5000 live male newborns is the frequently fatal genetic disease resulted from various mutations in DMD gene encoding dystrophin protein. About 70% of DMD-causing mutations are exon deletion leading to frameshift of open reading frame and dystrophin deficiency. To facilitate translating human DMD-targeting CRISPR therapeutics into patients, we herein establish a genetically humanized mouse model of DMD by replacing exon 50 and 51 of mouse Dmd gene with human exon 50 sequence. This humanized mouse model recapitulats patient’s DMD phenotypes of dystrophin deficiency and muscle dysfunction. Furthermore, we target splicing sites in human exon 50 with adenine base editor to induce exon skipping and robustly restored dystrophin expression in heart, tibialis anterior and diaphragm muscles. Importantly, systemic delivery of base editor via adeno-associated virus in the humanized male mouse model improves the muscle function of DMD mice to the similar level of wildtype ones, indicating the therapeutic efficacy of base editing strategy in treating most of DMD types with exon deletion or point mutations via exon-skipping induction. Duchenne muscular dystrophy (DMD) results from mutations in the DMD. Here the authors report using adenine base editing of exon splice sites to restore dystrophin expression and muscle function in a humanized mouse model of DMD with exon 50 and 51 of mouse DMD gene replaced with human exon 50.