Antisense-induced exon skipping restores dystrophin expression in DMD patient derived muscle cells

Due to frame-shifting mutations in the DMD gene that cause dystrophin deficiency, Duchenne muscular dystrophy (DMD) patients suffer from lethal muscle degeneration. In contrast, mutations in the allelic Becker muscular dystrophy (BMD) do not disrupt the translational reading frame, resulting in a less severe phenotype. In this study, we explored a genetic therapy aimed at restoring the reading frame in muscle cells from DMD patients through targeted modulation of dystrophin pre-mRNA splicing. Considering that exon 45 is the single most frequently deleted exon in DMD, whereas exon (45+46) deletions cause only a mild form of BMD, we set up an antisense-based system to induce exon 46 skipping from the transcript in cultured myotubes of both mouse and human origin. In myotube cultures from two unrelated DMD patients carrying an exon 45 deletion, the induced skipping of exon 46 in only approximately 15% of the mRNA led to normal amounts of properly localized dystrophin in at least 75% of myotubes. Our results provide first evidence of highly effective restoration of dystrophin expression from the endogenous gene in DMD patient-derived muscle cells. This strategy may be applicable to not only >65% of DMD mutations, but also many other genetic diseases.