Antisense oligonucleotide (ASO) mediated exon skipping aims to reframe dystrophin transcripts for patients with Duchenne muscular dystrophy (DMD). Currently 4 ASOs have been approved by the Food and Drug Administration targeting exon 45, 51 and 53 based on low level dystrophin restoration. Additional studies to confirm functional effects are ongoing. Furthermore, efforts are ongoing to increase muscle specific delivery of ASOs. Consequently, there are 5 clinical trials ongoing or planned for exon 51 skipping ASOs in Europe. While exon 51 skipping applies to the largest group of patients, DMD expert centers do not have sufficient numbers of patients or capacity to run all these trials in parallel. Even at a national level numbers may be too scarce. At the same time, some families now face the choice between participation in different clinical trials of exon 51 skipping, sometimes in addition to the choice of participating in a micro-dystrophin gene therapy trial. In this opinion paper, we outline the challenges, compare the different exon 51 skipping trials, and outline how different European centers and countries try to cope with running multiple trials in parallel for a small group of eligible patients.
Keywords: Duchenne muscular dystrophy; antisense oligonucleotide; clinical trial; dystrophin; exon 51 skipping.