ASsessing The REAl-world Safety & Effectiveness of Spinal Muscular Atrophy Participants Treated With Intrathecal Onasemnogene Abeparvovec-brve (OAV101B) (ITVISMA®): A U.S. Pragmatic Multicenter Study (STREAM)

Key Inclusion Criteria: A participant will be enrolled in STREAM only if all the following conditions are met: * The participant has a genetically confirmed diagnosis of SMA (biallelic SMN1 deletion or mutation). * He or she is ≥ 2 years of age on the day of the intrathecal injection. * The treating Investigator intends to administer within the current episode of care, a single dose of ITVISMA® (1.2 × 10¹⁴ vg) in routine U.S. practice after written informed consent obtained. * One of the following functional categories applies at screening: 1. independently ambulatory child/adolescent 2 - \<18 years; or 2. independently ambulatory adult (≥ 18 years). 3. non-ambulatory (includes walkers with assistance) adult \> 18 years with entry level RULM at baseline * At least 1 year of pre-treatment medical history, including motor-function documentation, can be retrieved from the site electronic record. Key Exclusion Criteria: A participant will be excluded if any of the following conditions apply: * Contraindication for lumbar puncture as determined by the investigator (e.g., spinal anatomy that precludes safe lumbar puncture) * An uncontrolled acute illness, active infection, febrile illness or acute medical condition, within 30 days prior to dosing * Inability to tolerate corticosteroids administered by mouth or gastrostomy tube * Current participation in another interventional clinical trial that would interfere with the objectives or endpoints of STREAM. Note: participation in observational cohort studies or non-interventional studies in which the participant does not receive treatment or undergo procedures which may compromise this study data integrity may be allowed following Sponsor approval * Planned relocation or any circumstance that is likely to prevent completion of the minimum 12-month follow-up. Other protocol inclusion, exclusion criteria may apply.