DMD and Duchenne muscular dystrophy: Two experimental drugs, eteplirsen (Sarepta Therapeutics, Cambridge, MA) and drisapersen (Prosensa Therapeutics, Leiden, the Netherlands and GlaxoSmithKline, Brentford, UK), are both designed to induce skipping of exon 51 (applicable to approximately 16% of DMD patients) and are being tested in phase II/III clinical trials.48,49 Although their oligonucleotide chemistries and side effect profiles differ, clinical trial data for both drugs show increased dystrophin expression in skeletal muscle biopsies of treated subjects.