Natural History Study to Characterise the Course of Disease Progression in Participants With Mucopolysaccharidosis Type IIIB

Inclusion Criteria

• •1. The participant has a definitive diagnosis of MPS IIIB, as determined by either of the following:
• •1. Documented deficiency in alpha-N-acetyl-glucosaminidase (NAGLU) enzyme activity or
• •2. Documented functionally-relevant mutations in both alleles of the NAGLU gene.
• •2. The participant is at least 1 year of age (biological age).
• •3. The participant or the participant's parent provides informed consent.
• •4. The participant is willing and able to comply with protocol requirements to the extent that may be expected of a participant with cognitive impairment.
• •In addition to the eligibility criteria above, a participant must meet all of the following criteria for Component 2:
• •1. The participant meets criterion a or criterion b below.
• •a. The participant is considered to be at risk of rapid disease progression based on at least 1 of the following criteria:
• •i. The participant has documented mutations of the NAGLU gene that are reported to be linked to rapid disease progression (for example, disease onset before 6 years of age), or
• •ii. The participant has a sibling, or other first- or second-degree relative with rapidly progressing MPS IIIB (for example, disease onset before 6 years of age).
• •b. The participant had disease onset prior to 6 years of age (biological age), as defined by:
• •i. Cognitive delay evaluated by Bayley Scales of Infant Development, Third Edition (BSID-III) or Kaufman Assessment Battery for Children, Second Edition (KABC-II), or
• •ii. Language delay, plateauing, or regression of language skills as determined by the Investigator (for example, participant uses isolated words, associated words such as 2-word combinations, sentences, poor or reduced language, and/or difficult to understand).
• •2. The participant has an age equivalent of ≥1 year on the Vineland Adaptive Behavior Scales, Second Edition (Vineland II).