Natural History Study of Patients With Mucopolysaccharidosis Type IIIB (MPS IIIB, Sanfilippo Syndrome Type B)

This is a multicenter longitudinal, prospective, natural history study of patients with
MPSIIIB designed to identify potential surrogate endpoints that may be utilized in future
Enzyme replacement therapy (ERT) trials of MPS IIIB via defined assessments including
standardized clinical, biochemical, neurocognitive, development, and imaging measures.

Inclusion Criteria:

Each patient must meet all of the following criteria to be enrolled in this study.

1. Definitive diagnosis of MPS IIIB, as determined by one of the following:

- Documented deficiency in NAGLU enzyme activity of ≤ 10% of the lower limit of
the normal range. OR

- Two documented mutations in the NAGLU gene.

2. The patient is ≥ 1 year of age and has an age equivalent on the Vineland Adaptive
Behavior Scales (VABS) of ≥ 1 year.

3. The patient is medically stable, in the opinion of the Investigator, to accommodate
the protocol requirements, including travel and assessments, without placing an undue
burden on the patient/patient's family.

4. The patient, patient's parent(s) or legal guardian(s) has voluntarily signed and
dated an Institutional Review Board/Independent Ethics Committee-approved informed
consent(assent if applicable) form after all relevant aspects of the study have been
explained and discussed with the patient, the patient's parent(s), or legal
guardian(s).

Exclusion Criteria:

Patients will be excluded from the study if they meet any of the following criteria at
screening:

1. Presence of significant non-MPS IIIB related central nervous system (CNS) impairment
or behavioral disturbances, sufficient, in the opinion of the Investigator, to
preclude performance of study neurocognitive and developmental testing procedures, or
that would confound the scientific integrity or interpretation of study assessments.

2. Visual or hearing impairment sufficient to preclude cooperation with
neurodevelopmental testing.

3. Patient has a known or suspected hypersensitivity to anesthesia or is thought to be
at an unacceptable risk from anesthesia, due to airway compromise or other
conditions, in the opinion of the Investigator.

4. Personal history or family history of neuroleptic malignant syndrome, malignant
hyperthermia, or other anesthesia-related concerns.

5. History of poorly controlled seizure disorder.

6. Currently receiving psychotropic or other medications, which in the Investigator's
opinion would be likely to substantially confound test results.

7. History of bleeding disorder, inability to abstain from medications that affect blood
clotting(e.g., aspirin, Non-steroidal anti-inflammatory drug (NSAIDs)), or history of
their ingestion within 1 week prior to a lumbar puncture.

8. History of complications from previous lumbar punctures that, in the opinion of the
Investigator, place the patient at increased risk from this procedure.

9. The patient is participating, plans to participate, or participated in a clinical
trial of another investigational medicinal product, or has received a vaccination,
within the 30 days prior to the study or for less than 5 half lives (whichever is
longer) of the investigational product.

10. History of hematopoietic stem cell or bone marrow transplant.

11. Unable to assent, or the patient's parent(s) or patient's legal guardian(s) is/are
unable to understand the nature, scope, and possible consequences of the study, or
do/does not agree to comply with the protocol defined schedule of assessments.

12. Patient is unable to comply with the protocol (e.g., has a clinically relevant
medical condition making implementation of the protocol difficult, unstable social
situation, or otherwise unlikely to complete the study) or is, in the opinion of the
Investigator, otherwise unsuited for the study.

13. The patient has any item (braces, tattoos, etc) which would exclude the patient from
being able to undergo MRI according to local Institutional Policy, or the patient has
any other situation that would exclude the patient from undergoing any other
procedure required in this study.

14. The patient is pregnant.