Muscle-specific gene editing improves molecular and phenotypic defects in a mouse model of Myotonic Dystrophy type 1

Therapeutic gene editing for treatment of monogenic diseases is a powerful technology that could in principle eliminate definitively the disease-causing genetic defect. The precision and efficiency of the molecular mechanisms are still under investigation in view of a possible use in clinical practice. Here we describe the application of the CRISPR/Cas9 strategy to remove the CTG-expansion in the DMPK gene causing myotonic dystrophy type 1 (DM1) in a mouse model carrying the human transgene from a DM1 patient. To optimize the editing efficiency in vivo, we identified new tools that allowed to improve the expression levels and the activity of the CRISPR/Cas9 machinery. Newly designed guide RNA pairs were tested in DM1-patient derived cells prior to in vivo application. Edited cells expressing the selected pair were analyzed to assess the occurrence of off- target and the accuracy of on-target genomic events. Systemic delivery of CRISP/Cas9 components through myotropic adeno- associated viral vectors led to significant improvement of molecular alterations in the heart and skeletal muscle. Importantly, a persistent increase of body weight, improvement of muscle strength and body composition parameters were observed in treated animals,