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

• Participants who are ambulatory. Ambulatory as defined as "being able to walkwithout the use of an assistive device."

• Established clinical diagnosis of DMD and documented dystrophin gene mutationpredictive of DMD phenotype confirmed by Sponsor genetic testing.

• Negative for AAV antibodies.

• On a stable dose of at least 0.5 mg/kg/day of oral daily prednisone or 0.75mg/kg/day deflazacort for ≥12 weeks prior to entering the study.

• Meet 10-meter walk/run time criteria

• Meet time to rise from supine criteria

• Participant has body weight: ≤50 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.