Extension Study of Intrathecal Enzyme Replacement for Cognitive Decline in MPS I

Inclusion Criteria:

1. The subject has completed the MIRC-002 study of intrathecal enzyme replacement therapy
for cognitive decline in mucopolysaccharidosis I

2. Age six years or older.

3. Subject and/or guardian willing and able to provide written informed consent.

4. Negative urine pregnancy test at screening (non-sterile females of child-bearing
potential only)

5. Currently using two acceptable methods of birth control as determined by the
investigator and willing to continue to use acceptable birth control during their
participation in the study (non-sterile females of child-bearing potential who are
sexually active only)

6. Willing and able to comply with study procedures. For example, the subjects must be
able to complete written and computer-based testing. The subjects must be able to lie
still in the MRI scanner for at least 40 minutes without sedation.

Exclusion Criteria:

1. The subject has undergone hematopoietic stem cell transplantation

2. Recent initiation of intravenous Aldurazyme® therapy with less than 6 months of
therapy. Subjects who have been receiving Aldurazyme® therapy for more than 6 months,
and those who have never received Aldurazyme® therapy, will be allowed to enroll

3. Pregnant or lactating, or considering pregnancy

4. Receipt of an investigational drug or procedure other than intrathecal Aldurazyme®
within 30 days of enrollment

5. A condition, medical or other, that prevents participation in the study, including
severe auditory or visual impairment, significant lumbar pathology, lumbar catheter,
or recent major surgery within 6 weeks that would preclude their ability to
participate.

6. Infusion reactions to intravenous or intrathecal Aldurazyme® therapy that are
life-threatening or require emergent intervention such as epinephrine, cardiopulmonary
resuscitation, or hospitalization

7. The subject has severely impaired spinal CSF flow, demonstrated by failure of
appearance of radionuclide in the basal cisterns by 4 hours after intra-lumbar
administration.

8. The subject has a coagulopathy, as identified by a platelet count of less than 50,000,
an INR of 1.5 or greater, or a PTT that is 1.5 times the upper limit of normal for the
laboratory from which it was drawn.