A Treatment Study of Mucopolysaccharidosis Type IIIB

Inclusion Criteria:

Individuals eligible to participate in Part 1 of this study must meet all of the following
criteria:

- Has deficient NAGLU enzyme activity at Screening. Blood for NAGLU enzyme activity will
be collected and analyzed centrally.

- Is ≥ 1 and < 11 years of age (at least 1 of the 3 subjects in Part 1 must be ≥ 1 and <
6 years of age)

- Has presented with signs/symptoms consistent with MPS IIIB; for individuals who have
not presented with signs/symptoms of disease (eg, siblings of known patients), the
determination of eligibility will be at the discretion of the BioMarin medical monitor
in conjunction with the site investigator.

- 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

Individuals eligible to participate in Part 2 of this study must meet all of the following
criteria:

- Participated in and met protocol requirements for transitioning from Study 250-901 or
participated in Part 1 of Study 250-201

- Written informed consent from parent or legal guardian and assent from subject, if
required

Exclusion Criteria:

Individuals who meet any of the following exclusion criteria are ineligible to participate
in Part 1 of the study:

- Has received stem cell, gene therapy or ERT for MPS IIIB

- Has contraindications for neurosurgery (eg, congenital heart disease, severe
respiratory impairment, or clotting abnormalities)

- Has contraindications for MRI scans (eg, cardiac pacemaker, metal fragment or chip in
the eye, or aneurysm clip in the brain)

- Has a history of poorly controlled seizure disorder

- Is prone to complications from intraventricular 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.

- Is pregnant at any time during the study

Individuals who meet any of the following exclusion criteria are ineligible to participate
in Part 2 of this study:

- Has received stem cell, gene therapy or ERT for MPS IIIB

- Has contraindications for neurosurgery (eg, congenital heart disease, severe
respiratory impairment, or clotting abnormalities)

- Has contraindications for MRI scans (eg, cardiac pacemaker, metal fragment or chip in
the eye, or aneurysm clip in the brain)

- Is prone to complications from intraventricular 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.

- Is pregnant at any time during the study