Termination of study by investigator related to COVID pandemic.

This is a five-year extension study of the pilot study, "Intrathecal Enzyme Replacement for Cognitive Decline in MPS I". Participants must have completed the pilot study to participate in this study.

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.

5 years, 6 months