Safety, Tolerability and Efficacy of ICV AX 250 Treatment in MPS IIIB -OLE

Inclusion criteria

• Must have completed 240 weeks of Study 250-202 and enter 250-401 within 8 weeks of dosing completion.
• Provides written informed consent from parent or legal guardian and assent from subject, if required
• Has the ability to comply with protocol requirements in the opinion of the investigator
• If female with childbearing potential, must have a negative pregnancy test at the Screening visit and be willing to have additional pregnancy tests during the study

Exclusion criteria

• Has (1) a cognitive age equivalent (AEq ) score ≤ 18 months, (2) a development quotient (DQ) score ≤ 20, and (3) no evidence of improvement during the 250-202 study in secondary or exploratory efficacy endpoints
• Would not benefit from enrolling in the study in the opinion of the investigator
• Has received stem cell, gene therapy or enzyme replacement therapy (other than AX 250) for MPS IIIB
• Has a history of poorly controlled seizure disorder
• Is prone to complications from ICV drug administration including patients 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 study
• Has a medical condition or extenuating circumstance that, in the opinion of the investigator, might compromise the subject's ability to comply with protocol requirements, the subject's well-being or safety, or the interpretability of the subject's clinical data