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

Phase 3, open-label, single-arm, single-dose, trial of onasemnogene abeparvovec-xioi (gene replacement therapy) in patients with spinal muscular atrophy (SMA) Type 1 who meet enrollment criteria and are genetically defined by a biallelic pathogenic mutation of the survival motor neuron 1 gene (SMN1) with one or two copies of survival motor neuron 2 gene (SMN2). 30 patients \< 6 months (\< 180 days) of age at the time of gene replacement therapy (Day 1) will be enrolled.

The trial includes a screening period, a gene replacement therapy period, and a follow-up period. During the screening period (Days -30 to -2), patients whose parent(s)/legal guardian(s) provide informed consent will complete screening procedures to determine eligibility for trial enrollment. Patients who meet the entry criteria will enter the in-patient gene replacement therapy period (Day -1 to Day 3). On Day -1, patients will be admitted to the hospital for pre-treatment baseline procedures. On Day 1, patients will receive a one-time intravenous (IV) infusion of onasemnogene abeparvovec-xioi, and will undergo in-patient safety monitoring over the next 48 hours. Patients may be discharged 48 hours after the infusion, based on Investigator judgment. During the outpatient follow-up period (Days 4 to End of Trial at 18 months of age), patients will return at regularly scheduled intervals for efficacy and safety assessments until the End of Trial when the patient reaches 18 months of age. After the End of Trial visit, eligible patients will be asked to participate into the long-term follow up trial.

All post-treatment visits will be relative to the date on which gene replacement therapy is administered, until the patient is 14 months of age, after which they will be relevant to the patient's date of birth.