The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of intracerebroventricular GC1123 in patients with MPS Ⅱ who have central nervous system involvement and are receiving treatment with intravenous drug

This study is designed as prospective, open-label, phase I and extension study. Safety, tolerability, pharmacokinetic, and pharmacodynamic properties of repeat-dose treatment of ICV-administered investigational product will be studied in patients undergoing standard treatments.

Patients will undergo cerebrospinal fluid (CSF) reservoir device implantation surgery on their scalps, and the reservoirs will be used to administer GC1123 to the cerebral ventricles monthly (every 28 days). The planned administering dose is 30 mg. After the 2nd dose on the 6th patient, Data and Safety Monitoring Boards (DSMB) will evaluate the safety and tolerability data of GC1123. The planned duration of the sutdy is total about 2 years (phase I and extension)

Inclusion Criteria:

1. Patient who has been diagnosed with severe MPS Ⅱ (Hunter syndrome)
2. Patient, aged 1.5 years (18 months) to 18 years at the time of the screening
3. Patient who has received and tolerated a minimum of 12 weeks of treatment with weekly intravenous treatment, and who has received 80% of the total planned infusions within that time frame.
4. Patient who is capable of undergoing neurosurgery, which has been confirmed by neurosurgeons and anesthesiologist.
5. Patient eligible to execute patient evaluation activities during the clinical trial period, as assessed by the investigator
6. Patient whose parents or legal representative are willing to participate in this clinical trial and provide written informed consent form

Exclusion Criteria:

1. Patient who has been administered with intrathecal Idursulfase in the past
2. Patient with a history of bone marrow transplantation or cord blood transplant
3. Patient with a history of ventriculoperitoneal shunt or other intracranial surgeries
4. Patient with end-stage multiple organ dysfunction syndrome or other severe diseases
5. Patient who is exposed to malignant neoplasm
6. Patient who has received treatment with any investigational drug or device within 30 days prior to study entry
7. Patient who have experience of hypersensitivity or anaphylaxis to ingredients of the investigational product at the time of screening
8. Patient with a history of bronchotomy/tracheostomy, or patient with acute respiratory disease at the time of screening
9. Patient who is ineligible to participate in the clinical trial due to laboratory test results or other reasons, as determined by the investigator