Gene Therapy Strategies For Myotonic Dystrophy Type 1

Background: Myotonic dystrophy type 1 (DM1) is a dominantly inherited neuromuscular disease caused by the abnormal expansion of CTG-triplets in the 3' untranslated region of the DMPK gene. While therapeutic approaches that neutralize the toxic DMPK transcript provide only short-term effects, CRISPR/Cas9-mediated gene editing strategies can eliminate permanently the pathogenic mutation. Methods and Results: Having previously applied CRISPR/Cas9-mediated gene therapy in DM1-patient-derived myogenic cells to eliminate the repeat expansion, we have recently employed a dual vector-mediated approach to transduce drug-inducible CRISPR/Cas9 complex components into DM1 patient-derived cells and DM1 mice carrying a mutated human DMPK transgene, either in skeletal muscle or systemically. These mice exhibit a pathologic neuromuscular phenotype and altered behavior similar to those observed in human disease. By using this strategy, we obtained efficient and inducible DMPK gene editing in the absence of off-target unintended events both in myogenic cells in vitro and in skeletal muscle tissues in vivo. Conclusions and Significance: CRISPR/Cas9-induced deletion of CTG expansion could potentially result in a durable therapeutic response in post-mitotic adult tissue, opening the way for future gene therapy application in humans. Importantly, the use of tissue-specific Cas9 and spatio-temporal control of gene editing minimizes unintended off-target activity.