Participant ambulatory status at the time of Screening Part A or Rescreening, as defined by the ability to complete a 10-meter walk/run test in \< 30 seconds:
* Cohorts 1, 2, and 4: Ambulatory
* Cohort 3: Either ambulatory or non-ambulatory
* Cohort 5: Non-ambulatory, but having been previously ambulatory by history
Established clinical diagnosis of DMD and documented dystrophin gene mutation predictive of DMD phenotype confirmed by Sponsor genetic testing. In cases where a genotype may be predictive of residual dystrophin production and/or a clear clinical diagnosis of DMD cannot be made (e.g., due to age), evaluation of dystrophin levels in baseline muscle biopsies may be required to determine eligibility under this criterion.
Negative for AAV antibodies.
Steroid regimen:
* Cohorts 1, 2, 4, and 5: A stable daily oral steroid regimen of at least 0.5 mg/kg/day of prednisone or 0.75 mg/kg/day of deflazacort for ≥12 weeks prior to Screening Part A or Rescreening, allowing for weight-based modifications consistent with clinical practice.
* Cohort 3: N/A
Meet 10-meter walk/run time criteria
Meet time to rise from supine criteria
Cohort 5: Meet Performance of Upper Limb (PUL) 2.0 criteria
Participant has body weight: ≤ 90 kg
You may not be if
Treatment with dystrophin modifying drugs within 3 months prior to screening.
Current or prior treatment with an approved or investigational gene transfer drug.
Exposure to certain approved or investigational drugs within 3 months prior to screening or 5 half-lives since last administration, whichever is longer.
Established clinical diagnosis of DMD that is associated with any deletion mutation invariant or variant predicted to not express exons 1 to 11 or, exons 42 to 45, or exons 57 to 69, inclusive, in the DMD gene as documented by a genetic report and confirmed by Sponsor genetic testing.
