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Exon skipping is a novel, mutation-specific approach to treating patients with Duchenne muscular dystrophy (DMD). Phosphorodiamidate morpholino oligomers are nucleic acid analogues that selectively redirect pre-mRNA splicing to enable production of internally truncated dystrophin.In exon 51 skipping (eteplirsen; n=36) and exon 53 skipping (golodirsen; n=25) clinical studies, internally shortened dystrophin mRNA was observed in all treated patients (per reverse transcription polymerase chain reaction). Eteplirsen increased dystrophin expression 15.5-fold, 11.6-fold, and 2.4-fold vs untreated controls (percent dystrophin-positive fibres, Western blot, and immunohistochemistry intensity, respectively; all, p≤0.007) in a 180 week study, and 2.8-fold (Western blot; p=0.008) in a 48 week study. Golodirsen increased dystrophin expression 10.7-fold (Western blot) over baseline following 48 weeks of treatment. Over 4 years, versus comparable external controls, eteplirsen slowed ambulatory decline (6 min walk test difference, 165 m; p=0.001) and cumulative risk of losing ambulation (83% vs 17%). In 2 clinical studies that included non-ambulatory patients, eteplirsen slowed pulmonary decline versus natural history data (assessed by spirometry).Eteplirsen and golodirsen demonstrated clinical and biochemical effects in patients with DMD; ongoing studies of these compounds are further characterising their effects in various patient populations.