Gene Transfer Clinical Trial for Mucopolysaccharidosis (MPS) IIIB

Inclusion Criteria: * Confirmed diagnosis of MPSIIIB by both of the following two methods: * No detectable or significantly reduced NAGLU enzyme activity by plasma. * Genomic DNA analysis demonstrating homozygous or compound heterozygous mutations in the NAGLU gene * Age: From Birth to 2 years or children older than 2 years with a minimum cognitive Development Quotient (DQ) of 60 or above (calculated by Bayley Scales of Infant and Toddler Development - Third Edition) Exclusion Criteria: * Inability to participate in the clinical evaluation as determined by Principal Investigator * Identification of two nonsense or null variants on genetic testing of the NAGLU gene * Has evidence of an attenuated phenotype of MPS IIIB * Presence of a concomitant medical condition that precludes lumbar puncture or use of anesthetics * Active viral infection based on clinical observations as infections by Adenoviruses, Epstein-Barr Virus, Cytomegalovirus, Respiratory Syncytial Virus * Concomitant illness or requirement for chronic drug treatment that in the opinion of the PI creates unnecessary risks for gene transfer , or precludes the child from participating in the protocol assessments and follow up as autoimmune diseases requiring immunosuppression, such as juvenile rheumatoid arthritis or idiopathic thrombocytopenia purpura * Subjects with total anti-AAV9 antibody titers ≥ 1:100 as determined by ELISA binding immunoassay * Subjects with a positive response for the ELISPOT for T-cell…