Dystrophin expression in the mdx mouse after localised and systemic administration of a morpholino antisense oligonucleotide

BACKGROUND: Duchenne and Becker muscular dystrophies are allelic disorders arising from mutations in the dystrophin gene. Duchenne muscular dystrophy is characterised by an absence of functional protein, while Becker muscular dystrophy is usually caused by in-frame deletions allowing synthesis of some functional protein. Treatment options are limited, and we are investigating the potential of transcript manipulation to overcome disease-causing mutations. Antisense oligonucleotides have been used to induce specific exon removal during processing of the dystrophin primary transcript and thereby by-pass protein-truncating mutations. The antisense oligonucleotide chemistry most widely used to alter pre-mRNA processing is 2'-O-methyl-modified bases on a phosphorothioate backbone. METHODS: The present studies evaluate 2'-O-methylphosphorothioate, peptide nucleic acid and morpholino antisense oligonucleotides in the mdx mouse model of muscular dystrophy, which has a nonsense mutation in exon 23 of the dystrophin gene. RESULTS: We demonstrate dystrophin expression in mdx mouse tissues after localised and systemic delivery of a morpholino antisense oligonucleotide designed to target the dystrophin exon 23 donor splice site. CONCLUSIONS: The stability of the morpholino structural type, and the fact that it can be delivered to muscle in the absence of a delivery reagent, render this compound eminently suitable for consideration for therapeutic exon skipping to address dystrophin mutations.