A Study of SGT-003 Gene Therapy in Duchenne Muscular Dystrophy (INSPIRE DUCHENNE)

Inclusion Criteria:

• Cohort 1: 4 to <7 years of age

• Cohort 2: 7 to <12 years of age

• Cohort 3: 0 to < 4 years of age

• Cohort 4: 12 to < 18 years of age

• Cohort 5: 10 to < 18 years of age

• Participant ambulatory status at the time of Screening Part A or Rescreening, asdefined 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 mutationpredictive of DMD phenotype confirmed by Sponsor genetic testing. In cases where agenotype may be predictive of residual dystrophin production and/or a clear clinicaldiagnosis of DMD cannot be made (e.g., due to age), evaluation of dystrophin levelsin baseline muscle biopsies may be required to determine eligibility under thiscriterion.

• Negative for AAV antibodies.

• Steroid regimen:

• Cohorts 1, 2, 4, and 5: A stable daily oral steroid regimen of at least 0.5mg/kg/day of prednisone or 0.75 mg/kg/day of deflazacort for ≥12 weeks prior toScreening Part A or Rescreening, allowing for weight-based modificationsconsistent 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

Exclusion Criteria:

• 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 toscreening or 5 half-lives since last administration, whichever is longer.

• Established clinical diagnosis of DMD that is associated with any deletion mutationin exons 1 to 11 or 42 to 45, inclusive, in the DMD gene as documented by a geneticreport and confirmed by Sponsor genetic testing.

Other inclusion or exclusion criteria apply.