Inclusion Criteria:

Has a diagnosis of MPS IIIB confirmed by deficient NAGLU enzyme activity analyzed at the laboratory during Screening.

Is ≥12 and ≤60 months of age with a BSID-III-C raw score ≥70. or Is >60 months of age regardless of cognitive level. Has provided written informed consent from a parent or legal guardian Has been determined by the investigator, after consultation with the participant (if applicable) and their family/caregiver, that the known risks of TA ICV infusion are outweighed by its potential benefits.

If female and of childbearing potential, agrees to follow contraception guidelines from screening until 30 days after the last dose of TA.

Has the ability to comply with program requirements, in the opinion of the investigator.

Exclusion Criteria:

Has contraindications for neurosurgery (e.g., congenital heart disease, severe respiratory impairment, or clotting abnormalities).

Has contraindications for MRI scans, if the investigator deems an MRI and not a CT scan is required for ICV access device placement or follow-up post-placement.

Has a history of poorly controlled seizure disorder. Is prone to complications from ICV infusion, including participants with hydrocephalus or ventricular shunts.

Has received any investigational medication within 30 days prior to the Baseline Visit or is scheduled to receive any investigational drug during the course of the program.

Has a medical condition or extenuating circumstance that, in the opinion of the investigator, might compromise the participant's ability to comply with program requirements, the participant's well-being or safety, or the interpretability of the participant's clinical data.