An Open-Label Study of UX003 Recombinant Human Beta-Glucuronidase (rhGUS) Enzyme Replacement Treatment in Mucopolysaccharidosis Type 7, Sly Syndrome (MPS 7) Patients Less Than 5 Years of Age

Inclusion Criteria:

1. Confirmed diagnosis of MPS 7 based on leukocyte or fibroblast glucuronidase enzyme
assay, or genetic testing.

2. Under 5 years of age at the time of informed consent.

3. Written informed consent of Legally Authorized Representative after the nature of the
study has been explained, and prior to any research-related procedures.

Exclusion Criteria:

1. Undergone a successful bone marrow or stem cell transplant or has evidence of any
degree of detectable chimaerism with donor cells.

2. Any known hypersensitivity to rhGUS or its excipients that, in the judgment of the
Investigator, places the subject at increased risk for adverse effects.

3. Use of any investigational product (drug or device or combination) other than UX003
within 30 days prior to Screening, or requirement for any investigational agent prior
to completion of all scheduled study assessments at any time during the study.

4. Has a condition of such severity and acuity, in the opinion of the Investigator, which
may not allow safe study participation. For patients with hydrops fetalis, the ongoing
interventions to manage fluid balance can be continued; if the addition of enzyme
replacement therapy (ERT) is considered a fluid-overload risk, the individual should
be excluded.

5. Has a concurrent disease or condition that, in the view of the Investigator, places
the subject at high risk of poor treatment compliance or of not completing the study,
or would interfere with study participation or affect safety. Since hydropic patients
have a high rate of mortality, the risk of death prior to 1 year of age should not be
considered sufficient to exclude the patient from the study for compliance.