A Long-Term Open-Label Treatment and Extension Study of UX003 rhGUS Enzyme Replacement Therapy in Subjects With MPS 7

Mucopolysaccharidosis type 7 (MPS 7, Sly syndrome) is an ultra-rare (< 100 cases currently
identified worldwide), chronically debilitating and life threatening lysosomal storage
disease. It is characterized by a deficiency of the lysosomal enzyme beta-glucuronidase
(GUS), required for degradation of the glycosaminoglycans (GAGs): dermatan sulfate (DS),
chondroitin-6-sulfate (CS) and heparan sulfate (HS). The GUS deficiency results in lysosomal
accumulation of GAGs in multiple tissues and organs throughout the body and numerous clinical
signs and symptoms as a result of tissue damage and organ dysfunction. There are currently no
approved treatments for MPS 7.

UX003 (recombinant human beta glucuronidase, rhGUS) is intended as a long-term enzyme
replacement therapy (ERT) for the treatment of MPS 7 via intravenous (IV) administration.
Ultragenyx is conducting this treatment and extension study to assess the long-term safety
and efficacy of UX003 treatment in subjects with MPS 7. Subjects with MPS 7 who are UX003
treatment-naïve or have been previously enrolled and treated with UX003 in other clinical
studies or programs are eligible for enrollment.

The study will continue for up to 144 weeks or until one of the following occurs: the subject
withdraws consent and discontinues from the study, the subject is discontinued from the study
at the discretion of the Investigator or Ultragenyx, or the study is terminated.

Inclusion Criteria:

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

- Willing and able to provide written, signed informed consent or, in the case of
subjects under the age of 18 (or 16 years, depending on the region), provide written
assent (if required) and written informed consent by a legally authorized
representative after the nature of the study has been explained, and prior to any
research-related procedures.

- Willing and able to comply with all study procedures.

- Sexually active subjects must be willing to use acceptable, highly-effective methods
of contraception while participating in the study and for 30 days following the last
dose.

- Females of childbearing potential must have a negative pregnancy test at Baseline and
be willing to have additional pregnancy tests during the study. Females considered not
of childbearing potential include those who have not experienced menarche, or have had
tubal ligation at least one year prior to completion of the primary study, or have had
total hysterectomy.

- For UX003 treatment-naïve subjects only, apparent clinical signs of lysosomal storage
disease as judged by the Investigator, including at least one of the following:
enlarged liver and spleen, joint limitations, airway obstruction or pulmonary
problems, limitation of mobility while still ambulatory.

- For UX003 treatment-naïve subjects only, elevated uGAG excretion at a minimum of
2-fold over normal.

- For UX003 treatment-naïve subjects only, aged 5 years and older.

Exclusion Criteria:

- If enrolled in a prior UX003 clinical study, the subject experienced safety-related
event(s) in the prior UX003 clinical study that, in the opinion of the Investigator
and sponsor, precludes resuming UX003 treatment.

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

- Presence or history of any hypersensitivity to rhGUS or its excipients that, in the
judgment of the Investigator, places the subject at increased risk for adverse
effects.

- Pregnant or breastfeeding at Baseline or planning to become pregnant (self or partner)
at any time during the study.

- Other than the use of UX003, use of any investigational product (drug or device or
combination) within 30 days prior to Baseline, or requirement for any investigational
agent prior to completion of all scheduled study assessments.

- Presence of a condition of such severity and acuity that, in the opinion of the
Investigator, warrants immediate surgical intervention or other treatment or may not
allow safe study participation.

- Concurrent disease or condition, or laboratory abnormality 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 introduce
additional safety concerns.