This is a long term, safety follow up study of patients in the AVXS-101-CL-101 gene replacement therapy clinical trial for SMA Type 1 delivering onasemnogene abeparvovec-xioi. Patients will roll over from the parent study into this long-term study for continuous safety monitoring for up to 15 years.

This is a long term, safety follow up study of patients in the AVXS-101-CL-101 gene replacement therapy clinical trial for SMA Type 1 delivering onasemnogene abeparvovec-xioi. Patients will roll over from the parent study into this long-term study for continuous safety monitoring for up to 15 years. The last visit of the parent study or early discontinuation from the parent study may serve as the visit at which the informed consent form process is conducted for the AVXS 101-LT-001 long term follow-up safety study. Patients will return annually for follow up study visits for five (5) years, and then will be contacted via phone annually for ten (10) years. Additionally, patient record transfers from their local physician and/or neurologist will be requested in conjunction with the annual study visits and phone contacts for review by the investigator.

If the patient is unable to return to the original investigative site, the sponsor will arrange with the patients' local established physician to serve as an additional investigator to conduct the required assessments.

This clinical trial information was submitted voluntarily under the applicable law and, therefore, certain submission deadlines may not apply. (That is, clinical trial information for this applicable clinical trial was submitted under section 402(j)(4)(A) of the Public Health Service Act and 42 CFR 11.60 and is not subject to the deadlines established by sections 402(j)(2) and (3) of the Public Health Service Act or 42 CFR 11.24 and 11.44.).

Inclusion Criteria:

1. Patient who received onasemnogene abeparvovec-xioi in the AVXS-101-CL-101 gene replacement therapy clinical trial for SMA Type 1.
2. Parent/legal guardian willing and able to complete the informed consent process, comply with study procedures and visit schedule.

Exclusion Criteria:

1. Parent/legal guardian unable or unwilling to participate in the long term follow up safety study.

Patients in the AVXS-101-CL-101 gene replacement therapy clinical trial for SMA Type 1 delivering onasemnogene abeparvovec-xioi will roll over from the previous study into the AVXS-101-LT-001 study for continuous safety monitoring for up to 15 years.