Translational and regulatory challenges for exon skipping therapies

Several translational challenges are currently impeding the therapeutic development of antisense-mediated exon skipping approaches for rare diseases. Some of these are inherent to developing therapies for rare diseases, such as small patient numbers and limited information on natural history and interpretation of appropriate clinical outcome measures. Others are inherent to the antisense oligonucleotide (AON)-mediated exon skipping approach, which employs small modified DNA or RNA molecules to manipulate the splicing process. This is a new approach and only limited information is available on long-term safety and toxicity for most AON chemistries. Furthermore, AONs often act in a mutation-specific manner, in which case multiple AONs have to be developed for a single disease. A workshop focusing on preclinical development, trial design, outcome measures and different forms of approval was organized by the regulatory models and biochemical outcome measures working groups of Cooperation of Science and Technology (COST) Action “Networking towards clinical application of antisense-mediated exon skipping for rare diseases” (www.exonskipping.eu). The workshop included participants from patient organisations, academia and members of staff from the European Medicine Agency and MEB. This statement paper contains the key outcomes of this meeting.