Leiden University Medical Center (LUMC) and Biotech Company Prosensa have announced positive results from the first clinical study with RNA-based therapeutic PRO051 in four patients with Duchenne Muscular Dystrophy (DMD). In the study, DMD patients between 10 and 13 years of age received a single injection of PRO051 (a 2-’O-methyl antisense oligonucleotide) in a small area of a muscle in the lower leg. In a biopsy taken four weeks later, novel dystrophin expression was observed in the vast majority of muscle fibers with protein levels that are expected to be clinically relevant. This study demonstrates clinical proof-of-mechanism that PRO051, based on Prosensa’s proprietary exon skipping technology, was able to correct this genetic error in locally injected muscle tissue of DMD patients. PRO051 will now enter systemic Phase I/II trials in order to investigate the effects and safety of PRO051 after repeated systemic injections and assess the broader benefits available to patients. These extremely promising results of the first human exon-skipping trial have raised much excitement and enthusiasm amongst the patient community. RNA-based therapeutics hold great promise as an approach to create a whole new class of innovative medicines.