Long-Term Safety, Tolerability, and Efficacy of DTX101 (AAVrh10FIX) in Adults With Moderate/Severe to Severe Hemophilia B

Hemophilia B is an X-linked recessive genetic bleeding disorder caused by mutations in the
factor IX (FIX) gene. FIX is produced in the liver and is critical for fibrin clot formation.
Hemophilia B is characterized by frequent, spontaneous internal bleeding that can lead to
chronic arthropathy (joint damage), intracranial hemorrhage, and even death. In patients with
moderate/severe to severe hemophilia B, the majority of bleeding episodes occur in the joints
and, if not treated, lead to debilitating damage and a decreased quality of life.

Study 101HEMB02 is a long-term follow-up study to evaluate the safety, tolerability, and
efficacy of AAVrh10-mediated gene therapy of human FIX in subjects with moderate/severe to
severe hemophilia B. The primary objective of the study is to determine the long-term safety
and efficacy of DTX101 following a single IV infusion (administered during Study 101HEMB01)
in adults with moderate/severe to severe hemophilia B.

This study was previously posted by Dimension Therapeutics, which has been acquired by
Ultragenyx.

Inclusion Criteria:

1. Willing and able to provide written informed consent.

2. Completed the Week 52 visit in Study 101HEMB01.

3. Willing to stop prophylactic treatment with recombinant FIX at specified time points
during the study if medically acceptable.

4. Willing, able, and committed to comply with scheduled study site visits, study
procedures, and requirements.

Exclusion Criteria:

1. Planned or current participation in another interventional clinical study that may
confound the efficacy or safety evaluation of DTX101 during the duration of this
study.

2. Any clinically significant medical condition that, in the opinion of the investigator,
would pose a risk to subject safety or would impede the study