Study of Intrathecal Idursulfase-IT Administered in Conjunction With Elaprase® in Pediatric Patients With Hunter Syndrome and Early Cognitive Impairment

Elaprase, a large molecular protein, is not expected to cross the blood brain barrier when
administered intravenously. A revised formulation of idursulfase, idursulfase-IT, that
differs from that of the intravenous (IV) formulation, Elaprase, has been developed to be
suitable for delivery into the cerebrospinal fluid (CSF) via intrathecal administration.

Mucopolysaccharidosis II (MPS II) is a rare, X-linked, inherited disease that affects males
nearly exclusively. The disease is caused by the absence of, or deficiency in, the activity
of the lysosomal enzyme, iduronate-2-sulfatase (I2S) which acts to cleave O-linked sulfate
moieties from the glycosaminoglycan (GAG) molecules dermatan sulfate and heparan sulfate.

Study HGT-HIT-094 is a controlled, randomized, two-arm, open-label, assessor-blinded,
multicenter study to determine the effect on clinical parameters of neurodevelopmental status
of monthly IT administration of idursulfase-IT 10 mg for 12 months in pediatric patients with
Hunter syndrome and cognitive impairment who have previously received and tolerated a minimum
of 4 months of therapy with Elaprase.

Pediatric patients under 3 years of age will be enrolled into a separate substudy to evaluate
the safety and efficacy of idursulfase-IT. The separate substudy is open label and single
arm. Patients who are enrolled in the substudy will receive idursulfase-IT treatment and
follow the same schedule of study visits.

Inclusion Criteria Inclusion Criteria for the Pivotal Study

Patients must meet all of the following criteria to be considered eligible for
randomization in the pivotal study:

1. The patient is male and is ≥3 and <18 years of age at the time of informed consent.

(Patients who are younger than 3 years of age may be enrolled in a separate substudy
provided that they meet other inclusion criteria, provided below.)

2. The patient must have a documented diagnosis of MPS II.

3. The patient has evidence at Screening of Hunter syndrome-related cognitive impairment
defined as follows:

A patient who is ≥3 and <13 years of age must have one of the following criteria (3a
OR 3b):

1. A GCA score ≥55 and ≤85 OR

2. If the patient has a GCA score at Screening >85, there must be evidence of a
decrease in GCA score of ≥10 points over 12 months from a previously documented
test result in observational study HGT-HIT-090.

A patient who is ≥13 and <18 years of age must have both of the following
criteria (3c AND 3d):

3. A GCA score of ≥55 and ≤85. AND

4. There must be evidence of a decrease in GCA score of ≥10 points over 12 months
from a previously documented

4. The patient has received and tolerated a minimum of 4 months of therapy with Elaprase
during the period immediately prior to Screening.

5. The patient must have sufficient auditory capacity, with a hearing aid(s), if needed,
in the Investigator's judgment to complete the required protocol testing and must be
compliant with wearing the hearing aid(s), if needed, on scheduled testing days.

6. The patient's parent(s) or legally authorized guardian(s) must have voluntarily signed
an Institutional Review Board/Independent Ethics Committee approved informed consent
form after all relevant aspects of the study have been explained and discussed.
Consent of the patient's parent(s) or legally authorized guardian(s) and the patient's
assent, if applicable, must be obtained prior to the start of any study procedures.

Inclusion Criteria for the Substudy

Patients must meet all of the following criteria to be considered eligible for enrollment
in the separate substudy:

1. The patient is male and is <3 years of age at the time of informed consent.

2. The patient must have a documented diagnosis of MPS II.

3. The patient has evidence at Screening of Hunter syndrome-related cognitive impairment

4. The patient has received and tolerated a minimum of 4 months of therapy with Elaprase
during the period immediately prior to Screening.

5. The patient must have sufficient auditory capacity, with a hearing aid(s), if needed,
in the Investigator's judgment to complete the required protocol testing and must be
compliant with wearing the hearing aid(s), if needed, on scheduled testing days.

6. The patient's parent(s) or legally authorized guardian(s) must have voluntarily signed
an Institutional Review Board/Independent Ethics Committee approved informed consent
form after all relevant aspects of the study have been explained and discussed.
Consent of the patient's parent(s) or legally authorized guardian(s) must be obtained
prior to the start of any study procedures.

Exclusion Criteria

Patients who meet any of the following criteria are not eligible to be randomized into the
pivotal study or enrolled in the separate substudy:

1. The patient has clinically significant non-Hunter syndrome-related CNS involvement
(such as Fragile-X syndrome) which is judged by the Investigator to be likely to
interfere with the accurate administration and interpretation of protocol assessments.

2. The patient has a large chromosomal deletion or complex rearrangement that includes a
deletion of the FMR1 and/or FMR2 genes.

3. The patient has a significant medical or psychiatric comorbidity(ies) that might
affect study data or confound the integrity of study results.

4. The patient has contra-indications for performance of lumbar puncture such as
musculoskeletal/spinal abnormalities or risk of abnormal bleeding.

5. The patient has a history of complications from previous lumbar punctures or technical
challenges in conducting lumbar punctures such that the potential risks would exceed
possible benefits for the patient.

6. The patient has an opening CSF pressure upon lumbar puncture that exceeds 30.0 cm H2O.

7. The patient has experienced infusion-related anaphylactoid event(s) or has evidence of
consistent severe adverse events related to treatment with Elaprase which, in the
Investigator's opinion, may pose an unnecessary risk to the patient.

8. The patient has received a cord blood or bone marrow transplant at any time or has
received blood product transfusions within 90 days prior to Screening.

9. The patient has a history of poorly controlled seizure disorder.

10. The patient is unable to comply with the protocol (eg, has significant hearing or
vision impairment, a clinically relevant medical condition making implementation of
the protocol difficult, unstable social situation, known clinically significant
psychiatric/behavioral instability, is unable to return for safety evaluations, or is
otherwise unlikely to complete the study), as determined by the Investigator.

11. The patient is enrolled in another clinical study that involves clinical investigation
or use of any investigational product (drug or [intrathecal/spinal] device) within 30
days prior to study enrollment or at any time during the study.

12. The patient has any known or suspected hypersensitivity to anesthesia or is thought to
be at an unacceptably high risk for anesthesia due to compromised airways or other
conditions.

13. The patient has a condition that is contraindicated as described in the SOPH-A-PORT
Mini S IDDD Instructions for Use (IFU), including but not limited to the presence of a
CSF shunt device in the patient.