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.

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.

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.

This is an 48-week open-label study to determine the efficacy and safety of AMONDYS 45, EXONDYS 51, VYONDYS 53 for the treatment of boys with duchenne muscular dystrophy who have a single exon duplication of either exon 45, 51 or 53, respectively. There will be weekly infusions and two muscle biopsies at baseline and at month 12.

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.

This arm will involve the treatment of boys with DMD who have a duplication of exon 45, for which AMONDYS 45 will target skipping of this exon.

This arm will involve the treatment of boys with DMD who have a duplication of exon 51, for which EXONDYS 51 will target skipping of this exon.

This arm will involve the treatment of boys with DMD who have a duplication of exon 53, for which VYONDYS 53 will target skipping of this exon.

Change in Dystrophin Expression From Baseline Following Treatment With Either AMONDYS 45 (Previously Casimersen), EXONDYS 51 (Previously Eteplirsen ), or VYONDYS 53 (Previously Golodirsen)

Change in Dystrophin Expression From Baseline Following Treatment With Either AMONDYS 45 (Previously Casimersen), EXONDYS 51 (Previously Eteplirsen ), or VYONDYS 53 (Previously Golodirsen).

Expression of dystrophin will be measured by immunofluorescent staining in muscle tissue sections in comparison to baseline values

Inclusion Criteria: Is a male with DMD and has an out-of-frame duplication of either exon 45, 51, or 53, with a normal copy number of all other DMD exons. Is above age 6 months of age. Has sufficient muscle mass in a pair of bilateral muscles that will allow for pre- and post-treatment muscle biopsies per PI discretion. If the subject is ambulant and 4 years old or greater and has been on a stable dose or dose equivalent of oral corticosteroids for at least 12 weeks prior to Week 1 the dose is expected to remain constant (except for modifications to accommodate changes in weight) throughout the study. Exclusion Criteria: Any additional missing exon for DMD that cannot be treated with study drugs. Other inclusion/exclusion criteria apply

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