Long-term Follow-Up for RGX-121

This is a prospective follow-up study to evaluate the long-term safety and efficacy after a single administration of RGX-121. Eligible participants are those who previously have enrolled in clinical study RGX-121-101 and received a single intracisternal (IC) or intracerebroventricular (ICV) infusion of RGX-121. Enrollment of each participant will occur the same day or after the participant has completed the end of study (EOS) visit or early termination visit (ET) from the previous (parent) study. Participants will be followed in this study cumulatively for up to 5 years after RGX-121 administration (inclusive of the parent study) or until RGX-121 is commercially available in the participant's country, whichever occurs first. No treatment will be directed under this observational protocol. The total study duration for each participant may vary depending on when they enroll in the current study following RGX-121 administration in the parent study.