Deletion of exons 45 to 55 in the DMD gene: from the therapeutic perspective to the in vitro model

Gene editing therapies in development for correcting out-of-frame DMD mutations in Duchenne muscular dystrophy aim to replicate benign spontaneous deletions. Deletion of 45-55 DMD exons (del45-55) was described in asymptomatic subjects, but recently serious skeletal and cardiac complications have been reported. Uncovering why a single mutation like del45-55 is able to induce diverse phenotypes and grades of severity may impact the strategies of emerging therapies. Cellular models are essential for this purpose, but their availability is compromised by scarce muscle biopsies. Here, we have introduced through CRISPR-Cas9 edition, a del45-55 mimicking the intronic breakpoints harboured by a subset of patients of this form of dystrophinopathy, into a Duchenne patients cell line. Dystrophin expression was restored in edited myoblasts and the myogenic defects were ameliorated. Besides confirming the potential of CRISPR-Cas9 to create tailored mutations as a useful approach to generate in vitro models, we also generated an immortalized myoblast line derived from a patient with a specific del45-55. Overall, we provide helpful resources to deepen into unknown factors responsible for DMD-pathophysiology. SUMMARY STATEMENTWe restored dystrophin expression in a DMD culture by replicating the exact deletion in exons 45-55 harboured by mild patients, testing this therapeutic approach, and creating a new cell model.