The main purpose of this study is to evaluate differences in the pharmacodynamic response of 4 Aldurazyme® (laronidase) dose regimens in patients with Mucopolysaccharidosis I (MPS I).

Inclusion Criteria:

• Have a documented diagnosis of MPS I, confirmed by measurable clinical signs and symptoms of MPS I, and a documented fibroblast or leukocyte α-L-iduronidase enzyme activity level of less than 10% of the lower limit of the normal range of the measuring laboratory.
• Weigh at least 12.5 kg.
• Have serum creatinine and blood urea nitrogen (BUN) values within age appropriate normal ranges.
• Provide signed, written informed consent prior to any protocol-related procedures being performed. Consent of a legally authorized guardian(s) is (are) required for patients under 18 years. If the patient is under 18 years old and can understand the consent, written informed consent will be required from both the patient and the authorized guardian(s).

Exclusion Criteria:

• Have previously received Aldurazyme® (laronidase).
• Have a suspected hypersensitivity to Aldurazyme® (laronidase) or known hypersensitivity to components of the infusion solution.
• Have previously undergone hematopoietic stem cell transplantation (HSCT; i.e., from bone marrow [BMT], peripheral blood, or umbilical cord blood) or other major organ transplantation.
• Have a medical condition, serious inter-current illness, or other extenuating circumstance that may interfere with study compliance including all prescribed evaluations and follow-up activities, except the 6MWT. (Note: All patients may not be capable of performing the 6MWT due to age and/or maturity level. Exemption from performing the 6MWT must be obtained in writing by the investigator from the sponsor's medical monitor prior to enrollment).
• Have an acute illness that requires surgical intervention, and/or anticipates surgery during study participation, and/or has had surgery within 30 days prior to study enrollment.
• Have received an investigational drug within 30 days prior to study enrollment.
• Is pregnant or lactating. Female patients of childbearing potential must have a negative pregnancy test [urine β-human chronic gonadotropin (hCG)] at entry (prior to the first infusion). Note: All female patients of childbearing potential and sexually mature males must be advised to use a medically accepted method of contraception throughout the study.

In multi-site studies, PI can publish after Genzyme publishes or 18 months after study completion. PI gives Genzyme a draft 60 days before publication. Genzyme can ask that confidential information be removed, and can defer publication another 60 days upon notifying PI that it will file a patent application on inventions contained in the draft.