Evaluation of Safety and Efficacy of Gene Therapy Drug in the Treatment of Spinal Muscular Atrophy (SMA) Type 2 Patients

Inclusion Criteria: Between 6 months and 60 months of age on day of signing informed consent form; Patient with SMA Type 2 as defined by the following features: Diagnosis of SMA based on gene mutation analysis with bi-allelic SMN1 mutations (deletion or point mutations) and 2 copies of SMN Onset of disease between 6 and 18 months of age Patient who can sit alone but never be able to stand or walk alone ; The 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 a previous gene therapy research trials; Patient who has received Nusinersen and Risdiplam treatment; Patient who has AAV9 neutralizing antibody titer ≥1:200; Patient with a point mutation in SMN2 (c.859G>C); Patient who requires non-invasive ventilatory support averaging≥12 hours/day at screening, or use invasive ventilatory support or pulse oximetry < 95% saturation while awake and calm at screening; Patient who is positive for human immunodeficiency virus (HIV) antibody, hepatitis B surface antigen, hepatitis C antibody, or treponema pallidum antibody; Abnormal laboratory values considered clinically significant, including gamma-glutamyl transferase(GGT), Aspartate aminotransferase (AST), alanine aminotransferase (ALT), bilirubin > 3x upper limit of normal (ULN), Hemoglobin (Hgb)< 110 or >150 g/L, platelet <lower limit of normal (LLN);Class IV patient based on Modified Ross Heart Failure Classification for Children; Patient with a history of glucocorticoid allergy; Contraindication that would interfere with the lumbar puncture procedures; Presence of an untreated active infection requiring systemic antiviral therapy at any time during the screening period; Vaccination less than 2 weeks before infusion of vector; Patient who has any concurrent clinically significant major disease or any other condition that, in the opinion of the Investigator, makes the subject unsuitable for participation in the study. Note: Other protocol defined inclusion/exclusion criteria may apply.