A Study to Evaluate the Safety and Tolerability of GEN6050X in Duchenne Muscular Dystrophy.

Prior treatment

• Received a live attenuated vaccine within 3 months prior to receiving GEN6050X, or was exposed to an influenza (or other inactivated) vaccine within 30 days prior to receiving GEN6050X, or received systemic antiviral, anti-infective, and/or interferon therapy.
• Severe infection (e.g., pneumonia, pyelonephritis, or meningitis) within 4 weeks prior to receiving gene therapy.
• Diagnosed with autoimmune disease or receiving related treatment for autoimmune disease.
• The titer of AAV9 neutralizing antibody determined by cell suppression assay \> 1:50.
• Patients have received any gene therapy (e.g., adeno associated virus(AAV) gene therapy), cell therapy (e.g., stem cell transplantation), in vivo editing, or ex vivo editing therapy (e.g., CRISPR-Cas9, TALEN) in the past.
• Participant has any contraindication to immunosuppressive therapy.

Other illness

• Participants are in the active period of viral infection, including infections such as TORCH virus, Epstein-Barr(EB) virus, and severe acute respiratory syndrome coronavirus 2 (SARS-COV-2).
• Serological tests found HIV, Hepatitis B Virus(HBV), hepatitis C virus(HCV), and syphilis infection.
• Has a medical condition or extenuating circumstance that, in the opinion of the principal investigator, is unsuitable for participation in the clinical trial.

Lab values

• With clear symptoms of cardiomyopathy, echocardiography shows that the left ventricular ejection fraction is less than 40%.
• The following indicators are abnormal in laboratory biochemical testing:
  • γ-glutamyl transpeptidase (GGT) above the 2-fold upper limit and total bilirubin above 1.5 times the upper limit, cystatin C (cystatin C) \> 1.27 mg/L, hemoglobin (Hgb) \< 100 or \>200 g/L; Leukocytes (WBC) \> 18.5×10\^9/L or platelet ≤ 125×10\^9/L.

Other

• Need for continuous or intermittent assisted support from a ventilator.
• The family does not wish to disclose the patient's study participation to the attending physician and other medical providers.

• Subject age: 4-10 years old (including 10 years old)
• Gender: Male
• Patients with DMD gene exon deletion types confirmed by molecular diagnosis: 8-49, 20-49, 22-49, 51, 51-53, 51-55, 51-57, 51-59, 51-60, 51-67, 51-69, 51-75 or 51-78 and other mutations amenable to exon 50 skipping.
• The participant is able to walk independently and completes the 10-meter walk test without assistance.
• Participant is able to complete time to stand from supine independently in less than 30s.
• The participant is able to cooperate with motor assessment testing.
• Receipt of glucocorticoids for 6 months and a stable daily dose for at least 12 weeks prior to study entry
• Ability to tolerate muscle biopsies under anesthesia with no contraindications to these procedures.