GB221 is a gene therapy that delivers a working SMN1 gene to the motor neurons of people with spinal muscular atrophy (SMA) Type 1. This study will evaluate the safety, tolerability and efficacy of GB221 in two groups:
1. participants aged from 2 weeks to younger than 12 months presenting with symptoms of SMA Type 1 who have never received a treatment OR are receiving the drug risdiplam 2. participants aged from 2 weeks to younger than 5 months who are at risk of developing SMA Type 1 (presymptomatic) and have never received treatment OR are receiving the drug risdiplam.
Symptomatic Participants
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
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
Any suspected or confirmed active viral infection at screening baseline (including HIV, Hepatitis B or C, or human T Cell lymphotropic viruses [HTLV])
History of invasive ventilatory support (tracheotomy with positive pressure) or pulse oximetry <95% saturation.
Ongoing immunosuppressive therapy or immunosuppressive therapy within 3 months of starting the trial (e.g. corticosteroids, cyclosporine, tacrolimus, methotrexate, cyclophosphamide, intravenous immunoglobulin, rituximab)
Participation in a recent SMA treatment clinical trial that, in the opinion of the Investigator, creates unnecessary risks for gene transfer.