Evaluation of Safety and Efficacy of Gene Therapy Drug in the Treatment of Spinal Muscular Atrophy (SMA) Type 3 Patients

Inclusion Criteria: * ≥2 years of age on the day of signing the informed consent form; * Genetic and clinical diagnosis of type 3 SMA with bi-allelic deletion of SMN1 of 5qSMA; * Hammersmith Functional Motor Scale - Expanded (HFMSE) score is between 10 and 54 at screening; * Female patients of childbearing age who are pregnant or lactating, as well as all enrolled patients （both male and female), should take effective contraceptive measures within 6 months after the treatment; * Patients or patient's legal guardian(s) must be able to understand the purpose and risks of the study and voluntarily provide signed and dated informed consent prior to any study-related procedures being performed. Exclusion Criteria: * Patient who has participated in any previous gene therapy research trials; * Patient who has AAV9 neutralizing antibody titer ≥1:200; * Patient who has received Nusinersen within 120 days and Risdiplam within 15 days before treatment; * Patient who requires invasive or non-invasive ventilatory support averaging≥16 hours/day at screening; * SMN2 copy numbers \>4； * Patient who needs nasal or gastric tube feeding for eating; * Patient who is positive for human immunodeficiency virus (HIV) antibody, hepatitis B surface antigen, hepatitis C antibody, or treponema pallidum antibody; * Known allergy or hypersensitivity to prednisolone or other glucocorticosteroids or their excipients * Severe contractures at screening that interfere with either the ability to attain/demon…