A Gene Transfer Therapy Study to Evaluate the Safety of and Expression From Delandistrogene Moxeparvovec (SRP-9001) in Participants With Duchenne Muscular Dystrophy (DMD) (ENDEAVOR)

A Gene Transfer Therapy Study to Evaluate the Safety of and Expression From Delandistrogene Moxeparvovec (SRP-9001) in Participants With Duchenne Muscular Dystrophy (DMD)

An Open-Label, Systemic Gene Delivery Study Using Commercial Process Material to Evaluate the Safety of and Expression From SRP-9001 in Subjects With Duchenne Muscular Dystrophy (ENDEAVOR)

This is an open-label gene transfer therapy study evaluating the safety of and expression from delandistrogene moxeparvovec in participants with DMD. The maximum participant duration for this study is 156 weeks.

Participants will receive a single intravenous (IV) infusion of delandistrogene moxeparvovec on Day 1.

Part 1: Change from Baseline in Quantity of Delandistrogene Moxeparvovec Dystrophin Expression at Week 12, as Measured by Western Blot

Part 1: Quantity of Delandistrogene Moxeparvovec Dystrophin Expression at Week 12 as Measured by Western Blot

Number of Participants With Treatment Emergent Adverse Events (TEAEs), Serious Adverse Events (SAEs) and Adverse Events (AEs) of Special Interest

Change from Baseline in Quantity of Delandistrogene Moxeparvovec Dystrophin Protein Expression at Week 12, as Measured by Immunofluorescence (IF) Fiber Intensity

Change from Baseline in Quantity of Delandistrogene Moxeparvovec Dystrophin Protein Expression at Week 12, as Measured by IF Percent Dystrophin Positive Fibers (PDPF)

Quantity of Delandistrogene Moxeparvovec Dystrophin Protein Expression at Week 12 as Measured by IF Fiber Intensity:

Quantity of Delandistrogene Moxeparvovec Dystrophin Protein Expression at Week 12 as Measured by IF PDPF

Inclusion Criteria: For Cohorts 1-7: Has a definitive diagnosis of DMD based on documented clinical findings and prior genetic testing. Cohort 1: Is ambulatory, and ≥4 to <8 years of age at the time of Screening. Cohort 2: Is ambulatory, and ≥8 to <18 years of age at the time of Screening. Cohort 3: Non-ambulatory per protocol specified criteria at the time of Screening. Cohort 4: Is ambulatory and ≥3 to <4 years of age at the time of Screening. Cohort 5a: Is ambulatory and ≥4 to <9 years of age. Cohort 5b: Non-ambulatory per protocol specified criteria at the time of Screening. Cohort 6: Is ambulatory, and ≥2 to <3 years of age at the time of Screening. Cohort 7: Non-ambulatory per protocol-specified criteria at the time of Screening. Ability to cooperate with motor assessment testing. Cohorts 1, 2, 3, 5, and 7 only: Stable dose equivalent of oral glucocorticoids for at least 12 weeks before screening and the dose is expected to remain constant (except for modifications to accommodate changes in weight) throughout the first year of the study. Cohorts 4 and 6: Do not yet require use of chronic steroids for treatment of their DMD, in the opinion of the Investigator, and are not receiving steroids at the time of Screening. rAAVrh74 antibody titers are not elevated as per protocol-specified requirements. Genetic mutation inclusion criteria vary by cohort. Exclusion Criteria: Has a concomitant illness, autoimmune disease, chronic drug treatment, and/or cognitive delay/impairment that in the opinion of the Investigator creates unnecessary risks for gene transfer. Exposure to gene therapy, investigational medication, or any treatment designed to increase dystrophin expression within protocol-specified time limits. Abnormality in protocol-specified diagnostic evaluations or laboratory tests. Other inclusion/exclusion criteria apply.