Personalised genetic intervention for Duchenne muscular dystrophy: antisense oligomers and exon skipping

Duchenne muscular dystrophy (DMD) arises from protein-truncating mutations in the large dystrophin gene that preclude synthesis of a functional protein that primarily stabilizes muscle fibre membranes. The absence of dystrophin leads to this most common and serious form of childhood muscle-wasting. Since the identification of the dystrophin gene in 1987, cell and gene repair or replacement therapies have been evaluated for DMD treatment and one genetic intervention, exon skipping, is now in clinical trials. Antisense oligomers have been designed to redirect dystrophin splicing patterns so that targeted exons may be removed from a defective dystrophin pre-mRNA to either restore the reading frame of a deletion, or excise an in-frame exon corrupted by a nonsense mutation or micro-insertion/deletion. This review discusses the evolution of oligomer induced exon skipping, including in vitro applications, evaluation of different oligomer chemistries, the treatment of animal models and alternative exon skipping strategies involving viral expression cassettes and ex vivo manipulation of stem cells. The discussion culminates with the current clinical trials and the great challenges that lie ahead. The major obstacle to the implementation of personalised genetic treatments to address the many different mutations that can lead to DMD, are considered to be establishing effective treatments for the different patients and their mutations. Furthermore, the view of regulatory authorities in assessing preclinical data on potentially scores of different but class-specific compounds will be of paramount importance in expediting the clinical application of exon skipping therapy for this serious and relentlessly progressive muscle wasting disease.