The main objective of this study is to evaluate the safety/tolerability and efficacy of UX111 (previously known as ABO-102) in participants with Mucopolysaccharidosis IIIA (MPS IIIA).

This is a multicenter, long-term follow-up study of patients with MPS IIIA who have participated in a prior clinical trial involving the administration of UX111 (NCT02716246 and NCT04088734). No investigational product will be provided. At approved sites adjuvant immunomodulatory (IM) therapy may be administered to selected participants. The Principal Investigator and/or caregiver, in consultation with the medical monitor, will determine whether to initiate adjuvant IM therapy. Not all participants may receive IM therapy.

This study was previously posted by Abeona Therapeutics, Inc and was transferred to Ultragenyx in August 2022.

Inclusion Criteria:

• Participants that have participated in a prior clinical trial in which they received UX111
• Parent(s)/legal guardian(s) of participant willing and able to complete the informed consent process and comply with study procedures and visit schedule

Exclusion Criteria:

• Planned or current participation in another clinical trial that may confound the safety or efficacy evaluation of UX111 during this study
• Any other situation or medical condition that precludes the participant from undergoing procedures required in this study