CRISPR-Cas9 correction in the DMD mouse model is accompanied by upregulation of Dp71f protein

Duchenne muscular dystrophy (DMD) is a severe hereditary disease caused by a deficiency in the dystrophin protein. The most frequent types of disease-causing mutations in the DMD gene are frameshift deletions of one or more exons. Pre-cision genome editing systems such as CRISPR-Cas9 have shown potential to restore open reading frames in numerous animal studies. Here, we applied an AAV-CRISPR double-cut strategy to correct a mutation in the DMD mouse model with exon 8-34 deletion, encompassing the N-terminal actin-bind-ing domain. We report successful excision of the 100-kb genomic sequence, which includes exons 6 and 7, and partial improvement in cardiorespiratory function. While corrected mRNA was abundant in muscle tissues, only a low level of trun-cated dystrophin was produced, possibly because of protein instability. Furthermore, CRISPR-Cas9-mediated genome ed-iting upregulated the Dp71f dystrophin isoform on the sarco-lemma. Given the previously reported Dp71-associated muscle pathology, our results question the applicability of genome ed-iting strategies for some DMD patients with N-terminal muta-tions. The safety and efficacy of CRISPR-Cas9 constructs require rigorous investigation in patient-specific animal models.