title: Induction of revertant fibres in the mdx mouse using antisense oligonucleotides.
abstract: BACKGROUND
  Duchenne muscular dystrophy is a fatal genetic disorder caused by dystrophin gene mutations that result in premature termination of translation and the absence of functional protein. Despite the primary dystrophin gene lesion, immunostaining studies have shown that at least 50% of DMD patients, mdx mice and a canine model of DMD have rare dystrophin-positive or 'revertant' fibres. Fine epitope mapping has shown that the majority of transcripts responsible for revertant fibres exclude multiple exons, one of which includes the dystrophin mutation.
  
  
  METHODS
  The mdx mouse model of muscular dystrophy has a nonsense mutation in exon 23 of the dystrophin gene. We have shown that antisense oligonucleotides (AOs) can induce the removal of this exon, resulting in an in-frame mRNA transcript encoding a shortened but functional dystrophin protein. To emulate one exonic combination associated with revertant fibres, we target multiple exons for removal by the application of a group of AOs combined as a "cocktail".
  
  
  RESULTS
  Exons 19-25 were consistently excluded from the dystrophin gene transcript using a cocktail of AOs. This corresponds to an alternatively processed gene transcript that has been sporadically detected in untreated dystrophic mouse muscle, and is presumed to give rise to a revertant dystrophin isoform. The transcript and the resultant correctly localised smaller protein were confirmed by RT-PCR, immunohistochemistry and western blot analysis.
  
  
  CONCLUSIONS
  This work demonstrates the feasibility of AO cocktails to by-pass dystrophin mutation hotspots through multi-exon skipping. Multi-exon skipping could be important in expediting an exon skipping therapy to treat DMD, so that the same AO formulations may be applied to several different mutations within particular domains of the dystrophin gene.
authors.affiliation: Experimental Molecular Medicine Group, Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Nedlands, Perth, 6009, Western Australia. afall@cyllene.uwa.edu.au
authors.forename: Abbie M
authors.initials: AM
authors.lastname: Fall
authors.forename: Russell
authors.initials: R
authors.lastname: Johnsen
authors.forename: Kaite
authors.initials: K
authors.lastname: Honeyman
authors.forename: Pat
authors.initials: P
authors.lastname: Iversen
authors.forename: Susan
authors.initials: S
authors.lastname: Fletcher
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Wilton