Abstract Title
Early expression of delCH1 dystrophin isoform reverse or prevents muscular dystrophy in the Dup2 mouse

Research Category
Gene Therapy

Author(s)
Nicolas Wein
Nicolas Wein, Ph.D.1, Adeline Vulin, Ph.D.1, Tabatha Simmons1, Felecia Gumienny1, Jacqueline Yurkoski1, Nianyuan Huang1, Robert Weiss, Ph.D.2 and Kevin Flanigan, M.D.1,2,3.
1Center for Gene Therapy, Nationwide Childrens Hospital, Columbus, OH;
2Department of Human Genetics, The University of Utah School of Medicine, Salt Lake City, UT;
3Departments of Pediatrics and 4Neurology, Ohio State University, Columbus, OH

Abstract
We recently demonstrated that truncation of the dystrophin reading frame upstream of exon 5 induces alternate translation initiation from an internal ribosome entry site (IRES) which is active in the absence of exon 2 but not in the presence of a duplicated exon 2. The resulting N-truncated dystrophin (delCH1) is highly functional as demonstrated both in patients expressing it and in our DMD mouse model carrying a duplication of exon 2 (Dup2) in which expression of the delCH1 protein reduces muscle deficiency despite lacking half of the actin-binding domain 1. We investigated whether this isoform is functional in all skeletal muscle by forcing it expression following intravascular injection of an AAV9.U7snRNA exon-skipping vector targeted toward exon 2. This results in high expression of delCH1 at 4weeks post-injection in all skeletal muscles, along with heart and diaphragm. Expression results in correction of the physiologic and pathologic features. Consistent with correction, a genome-wide normalized ribosome protected fragment (RPF)-Seq data analysis demonstrated restoration of global gene expression from a pattern associated with dystrophic muscle to a non-dystrophic pattern. Finally, we explored if early induction of this protein could prevent the development of dystrophic pathology. We injected Dup2 mice at postnatal day 1 (P1) and demonstrated that at three months, 6months and 1 year following injection, no sign of dystrophic histopathology was seen. In addition, muscle physiology was greatly improved. All this work strongly supports the idea that this isoform is highly functional, and that the induction of this protein should be beneficial for the 6% of patients with mutations within the first five exons of DMD. In addition, this study pave the way toward an early injection in DMD patient, which is now feasible since newborn screening for DMD is performed.