Ultragenyx Discontinues Wilson Disease Gene Therapy Program

FOR IMMEDIATE RELEASE

November 4, 2026

The Wilson Disease Association (WDA) is disappointed to share that Ultragenyx Pharmaceutical Inc. has announced its decision to discontinue further development of UX701, an investigational gene therapy for Wilson disease.

The decision follows additional results from the Cyprus2+ clinical study, which enrolled 20 Wilson disease patients in four groups receiving different doses of UX701. Although some patients experienced improvements in laboratory measurements related to copper levels, the results were not consistent across the groups. The highest-dose group also did not demonstrate substantial additional benefit compared with earlier groups.

Several patients were able to stop taking their standard Wilson disease medications and maintain acceptable copper levels for several years. However, the study did not meet its goal of showing that most patients could achieve the desired laboratory results and stop taking their standard-of-care medications.

Ultragenyx emphasized that the decision to discontinue development was based on insufficient effectiveness, not safety concerns. The investigational therapy was generally well tolerated and has demonstrated an acceptable safety profile to date.

“The data show that gene therapy can have a benefit for patients with Wilson disease,” said Andrew Grimm, MD, PhD, Vice President of Global Clinical Development for Metabolic Diseases, Ultragenyx. “Some investigators say it has been life-changing for some patients who experienced more energy and improvements in tremor and speech. But we hoped to see a greater overall benefit in the higher dose group and biomarker improvement.”

While this program will not move forward, the Wilson Disease Association’s commitment to advancing research and expanding treatment options for people living with Wilson disease remains as strong as ever.

“This is not the outcome we had hoped for, especially for the patients and families who courageously participated in the clinical trial of this investigational therapy,” said Rhonda Rowland, President of the Wilson Disease Association. “I’m deeply grateful to everyone who put their hopes in the study, as well as the investigators and research teams who dedicated so much time and effort to it. Ultragenyx has been an excellent partner to the Wilson disease community, and I appreciate their commitment to continue following these patients and sharing what they learn. That knowledge will help move the field forward.”

Ultragenyx has stated that patients who received UX701 will continue to receive long-term safety monitoring. Study investigators will contact participants and their families directly about next steps.

“While we’re disappointed, this isn’t the end of the road,” said Frederick Askari, MD, PhD, Director of the Wilson Disease Center of Excellence at the University of Michigan and principal investigator for the Cyprus2+ clinical trial. “Like many new developments, we learn from what has happened and move forward with better approaches. Some patients saw a real benefit. The company will keep following these patients to see how they do over time, and what we’ve learned will be shared with patients and the broader community. The patients who took part made a great contribution to moving the field forward, and I wouldn’t be surprised to see improved technologies come out of this work.”

Clinical research requires considerable time, dedication, and collaboration. Even when an investigational therapy does not advance, the experience and information gained can help inform future research efforts. Ultragenyx plans to publish a scientific manuscript and present the study results at a medical or scientific congress in 2027.

The WDA remains committed to supporting research, encouraging clinical trial participation, and advocating for the development of safe and effective new treatments for everyone affected by Wilson disease.

Community members with questions about the UX701 program may contact Ultragenyx at patientinquiry@ultragenyx.com.

For further details, read this community update letter from Ultragenyx.

About the Wilson Disease Association

The Wilson Disease Association is a 501(c)(3) nonprofit patient advocacy organization that provides support and hope to people affected by Wilson disease worldwide so they may achieve the best possible quality of life. To learn more, visit wilsondisease.org.

Media contact:
Christopher Peterson
Communications Manager
Wilson Disease Association
617.823.2618
chris.peterson@wilsonsdisease.org