The study will evaluate safety and efficacy of intrathecal delivery of GC101 gene therapy drug as a treatment of spinal muscular atrophy Type 2 (SMA 2) patients.

The purpose of this trial is to evaluate safety and efficacy of gene therapy drug GC101 in SMA 2 patients. Open-label, dose-escalation clinical trial of GC101 will be conducted in multiple centers in China.

GC101 will be administrated intrathecally. Short-term safety will be evaluated in 52 weeks and enter long-term follow-up study of 5 years at will. Patients will be tested at baseline and followed up on various time points.

The primary analysis for efficacy will be assessed at 12 months after treatment with GC101 on the motor milestone of stand unassisted for at least 3 seconds for patients of age between 6 and 24 months, or changes from baseline HFMSE scores for patients of age between 24 and 60 months.

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 any previous gene therapy research trials;
• Patient who has received Nusinersen within 4 months and Risdiplam within 15 days before 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 \