Inclusion Criteria:
Participants meeting all of the following criteria may be considered for inclusion:
1. Male, aged 5 to 10 years (inclusive).
2. Diagnosis of Duchenne Muscular Dystrophy (DMD) confirmed through medical history and genetic testing, characterized by a frameshift mutation (deletion or duplication) or a premature stop codon mutation in the DMD gene between exons 18 to 58.
3. Below-average performance on motor assessment testing.
4. Ability to cooperate with motor assessment testing.
5. Tolerance for muscle biopsy under anesthesia with no contraindications for biopsy.
6. Participants must have been taking a stable dose of oral corticosteroids for at least 12 weeks prior to screening, and the expected dose should remain constant throughout the study, except for adjustments related to changes in body weight.
Exclusion Criteria:
Participants meeting any one of the following criteria are not eligible for inclusion:
1. Active viral infection based on clinical observations.
2. Signs of cardiomyopathy, including echocardiogram with ejection fraction below 40%.
3. Serological evidence of HIV infection, or Hepatitis B or C infection.
4. Diagnosis of (or ongoing treatment for) an autoimmune disease.
5. Abnormal laboratory values considered clinically significant (GGT \> 3XULN, bilirubin ≥ 3.0 mg/dL, creatinine ≥ 1.8 mg/dL, Hgb \< 80 or \> 180 g/L; WBC \> 18.5\*10\^9/L).
6. Concomitant illness or requirement for chronic drug treatment that in the opinion of the PI creates unnecessary risks for gene transfer.
7. Subjects with AAVrh74 neutralizing antibody titers \> 1:400 as determined by ELISA immunoassay.
8. Has a medical condition or extenuating circumstance that, in the opinion of the investigator, might compromise the subject's ability to comply with the protocol required testing or procedures or compromise the subject's wellbeing, safety, or clinical interpretability.
9. Severe infection (eg. pneumonia, pyelonephritis, or meningitis) within 4 weeks before gene transfer visit (enrollment may be postponed).
10. Has received any investigational medication (other than corticosteroids) or exon skipping medications (including ExonDys 51), experimental or otherwise, in the last 6 months prior to screening for this study.
11. Has had any type of gene therapy, cell based therapy (eg. stem cell transplantation), or CRISPR/Cas9.
12. Family does not want to disclose patient's study participation with primary care physician and other medical providers
