A 48-Week, Open Label, Study to Evaluate the Efficacy and Safety of AMONDYS 45, EXONDYS 51, VYONDYS 53 in Subjects With DuchenneMuscular Dystrophy Carrying Eligible DMD Duplications.

DMD is a rare, serious, debilitating, and ultimately fatal, disease for which there is an urgent need to develop safe and effective therapies. In order to efficiently meet this urgency and the needs of the subject community, the study evaluates the efficacy and safety of AMONDYS 45, EXONDYS 51, VYONDYS 53 administration over approximately 1 year in DMD subjects with duplication mutations amenable to treatment by exon 45, 51 or exon 53 skipping. Skipping of a single copy of the duplicated exon is expected to result in a wild-type (WT) DMD transcript allowing the expression of a WT, full length dystrophin protein. Successful skipping of a single copy of the duplicated exon in in vitro and in vivo models has been reported in the literature. AMONDYS 45, EXONDYS 51, VYONDYS 53 have the potential to be disease-modifying treatments for boys with DMD mutations amenable to exon 45, 51 and exon 53 skipping, respectively.

The totality of the non-clinical data with these PMOs as well as AVI-4225 (targeting exon 23) and EXONDYS 51 suggests that PMOs are well tolerated in the non-clinical setting. Moreover, treatment with EXONDYS 51(at 30 mg/kg and 50 mg/kg) has been well-tolerated by boys with DMD deletion mutations amenable to skipping exon 51. The relatively low expected risk for subjects exposed to AMONDYS 45, EXONDYS 51, VYONDYS 53 and the urgent medical need for a treatment for this subject population support the conclusion that the potential benefits of exposing subjects to AMONDYS 45, EXONDYS 51, VYONDYS 53 outweigh the potential risks.