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

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.