Pre-Symptomatic Study of Intravenous Onasemnogene Abeparvovec-xioi in Spinal Muscular Atrophy (SMA) for Patients With Multiple Copies of SMN2

Phase 3, open-label, single-arm study of a single, one-time dose of onasemnogene abeparvovec-xioi (gene replacement therapy) in patients with spinal muscular atrophy who meet enrollment criteria and are genetically defined by bi-allelic deletion of survival motor neuron 1 gene (SMN1) with 2 or 3 copies of survival motor neuron 2 gene (SMN2). Patients with SMN1 point mutations or the SMN2 gene modifier mutation (c.859G\>C) may enroll but will not be included in the efficacy analysis sets.

The study 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 undergo screening procedures to determine eligibility for study enrollment. Patients who meet the entry criteria will enter the in-patient gene replacement therapy period (Day -1 to Day 2). On Day -1, patients will be admitted to the hospital for pre-treatment baseline procedures. On Day 1, patients will receive a single, one-time intravenous (IV) infusion of onasemnogene abeparvovec-xioi, and will undergo in-patient safety monitoring for a minimum of 24 hours post infusion. Patients may be discharged 24 hours (48 hours in Japan) after the infusion, based on Investigator judgment. During the outpatient follow-up period (Days 3 to End of Study at 18 or 24 of age, dependent upon respective SMN2 copy number), patients will return at regularly scheduled intervals for efficacy and safety assessments until the End of Study when the patient reaches 18 months of age (SMN2 = 2) or 24 months of age (SMN2 = 3). After the End of Study visit, eligible patients will be invited to rollover into a long-term follow up study.