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

Inclusion Criteria: * Cohort A participants: 3 months to 3 years of age, inclusive * Cohort B participants: 4 to 7 years of age, inclusive * Definitive diagnosis of DMD based on documented clinical findings and prior genetic testing. * Ability to cooperate with motor assessment testing. * Cohort A participants: No previous treatment with corticosteroids. * Cohort B participants: Stable dose equivalent of oral corticosteroids for at least 12 weeks prior to screening and the dose is expected to remain constant (except for potential modifications to accommodate changes in weight) throughout the first year of the study. * Cohorts A \& B: A frameshift mutation contained between exons 18 and 58 (inclusive). Exclusion Criteria: * 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. * Presence of any other clinically significant illness, medical condition, or requirement for chronic drug treatment that in the opinion of the Investigator creates unnecessary risk for gene transfer. Other inclusion or exclusion criteria could apply.