Study of Safety, Tolerability and Efficacy of GB221 in Infants With Spinal Muscular Atrophy Type 1

Inclusion Criteria: * Symptomatic Participants 1. Diagnosis of SMA Type 1 based on gene mutation analysis with bi-allelic SMN1 mutations (deletion or point mutations) and up to 3 copies of SMN2 2. Participants must be 2 weeks to \< 12 months of age at the time of dosing with disease onset of during the first 6 months of life. * Presymptomatic Participants 1. At risk of SMA Type 1 based on gene mutation analysis with bi-allelic SMN1 mutations (deletion or point mutations) and up to 2 copies of SMN2 2. Participants must be 2 weeks to \< 5 months (\< 150 days) of age at the time of dosing. Exclusion Criteria: 1. Any suspected or confirmed active viral infection at screening baseline (including HIV, Hepatitis B or C, or human T Cell lymphotropic viruses \[HTLV\]) 2. History of invasive ventilatory support (tracheotomy with positive pressure) or pulse oximetry \<95% saturation. 3. Ongoing immunosuppressive therapy or immunosuppressive therapy within 3 months of starting the trial (e.g. corticosteroids, cyclosporine, tacrolimus, methotrexate, cyclophosphamide, intravenous immunoglobulin, rituximab) 4. Participation in a recent SMA treatment clinical trial that, in the opinion of the Investigator, creates unnecessary risks for gene transfer. 5. Prior history of gene therapy for any indication, hematopoietic transplant or solid organ transplant 6. Subjects with severe scoliosis 7. Known allergy or hypersensitivity to prednisolone or other glucocorticosteroids or their excipients.