Single-Dose Gene Replacement Therapy Clinical Trial for Participants With Spinal Muscular Atrophy Type 1

Inclusion Criteria: * Patients with SMA Type 1 as determined by diagnosis of SMA based on gene mutation analysis with biallelic SMN1 mutations (deletion or point mutations) and one or two copies of SMN2 \[inclusive of the known SMN2 gene modifier mutation (c.859G\>C)\] * Patients must be \< 6 months (\< 180 days) of age at the time of onasemnogene abeparvovec-xioi infusion * Patients must have a swallowing evaluation test performed prior to administration of gene replacement therapy Exclusion Criteria: * Previous, planned or expected scoliosis repair surgery/procedure prior to 18 months of age * Use of invasive ventilatory support (tracheotomy with positive pressure) or pulse oximetry \< 95% saturation at screening * Use or requirement of non-invasive ventilatory support for 12 or more hours daily in the two weeks prior to dosing * Patient with signs of aspiration based on a swallowing test or whose weight-for-age falls below the 3rd percentile based on World Health Organization (WHO) Child Growth Standards and unwilling to use an alternative method to oral feeding * Participation in recent SMA treatment clinical trial (with the exception of observational cohort studies or non-interventional studies) or receipt of an investigational or commercial compound, product or therapy administered with the intent to treat SMA (eg, nusinersen, valproic acid,) at any time prior to screening for this trial.