This is an intermediate-size patient population Early Access Program (EAP) providing access to intracerebroventricular (ICV) tralesinidase alfa (TA) for participants with mucopolysaccharidosis type IIIB (MPS IIIB, Sanfilippo Syndrome Type B). The primary objectives are to allow early access to TA treatment and to evaluate the safety and tolerability of TA ICV infusion. Approximately 10 participants will be enrolled at up to 3 US sites and treated with TA once weekly via ICV infusion for up to approximately 52 weeks, or until TA becomes commercially available.