Abstract for presentation at 11th International Congress of Human Genetics

Duchenne muscular dystrophy (DMD) is an X-linked fatal muscle wasting disease caused by mutations in the dystrophin gene. A canine model of this disease, the Golden Retriever model of muscular dystrophy (GRMD), was used to examine the application of antisense oligonucleotides (AOs) to alter splicing of the dystrophin pre-mRNA to restore the reading frame and reestablish synthesis of a semi-functional protein.
The GRMD animal has a splicing mutation in intron 6 of the dystrophin gene that causes exon 7 to be excluded from the mRNA, resulting in a frame-shift that produces a prematurely truncated protein. Removal of the flanking exons 6 and 8 through AO targeted exon skipping would correct the GRMD dystrophin mRNA reading frame and restore translation of a near full length protein. A comparison of the efficacy of 2’-O-methyl phosphorothioate (2OME) AOs, phosphorodiamidate morpholino oligomers (PMOs) and cell penetrating peptide conjugated PMOs (PMO-Pep) to induce exon 6 and 8 skipping was performed in vitro and in vivo.
Each of the AO chemistries induced correction of the dystrophin mRNA reading frame in vitro in cultured myoblasts. However, only the PMO chemistries were able to induce dystrophin protein in vivo. Increased numbers of dystrophin positive fibres were observed in affected GRMD pups following a single intramuscular injection of PMOs or PMO-Peps.
In this study we have demonstrated that AO induced exon skipping can be used to restore dystrophin production in a highly relevant animal model of DMD. This should facilitate the testing of AO delivery regimens prior to application in human trials. Ultimately, it is hoped that DMD patients could be treated by AOs to produce a semi-functional protein, similar to that observed in some cases of the milder Becker muscular dystrophy.