Shionogi to End Zatolmilast Open-Label Extension for Adolescents
Shionogi has shared an important update on its clinical development program for zatolmilast in Fragile X syndrome. The company is discontinuing participation in its open-label extension (OLE) study, EXPERIENCE-302, for adolescents ages 17 and under. The study will remain open for adult participants, including eligible participants from the adolescent study.
Participants from the adolescent study who are currently enrolled in the OLE and are 18 years of age or older by October 31, 2026, may continue without changes or interruptions.
Following additional review and analysis, Shionogi concluded that the measures used to evaluate treatment effectiveness did not detect a positive treatment signal in the adolescent population. Shionogi reports that there have been no new safety findings.
As we reported in our May update, neither the adult nor the adolescent study met its originally specified primary endpoint.
We are deeply disappointed by this news, particularly for families whose children will no longer be able to continue in the study. We recognize the hope, time, and effort that participants and their caregivers have invested in this research, and we are grateful for their contributions.
Study sites will work directly with participating families and caregivers to support study completion and answer questions about treatment discontinuation, study procedures, and next steps. Families should look to their study investigators and site personnel for details specific to their participation.
Shionogi will continue analyzing data from adult participants in the OLE and discussing the data from the zatolmilast development program with the U.S. Food and Drug Administration.
At FRAXA, we are learning from this experience and will use these lessons to advance effective treatments and, ultimately, a cure for Fragile X syndrome. We will continue to share updates with the community as more information becomes available.
Shionogi’s full community letter is available below. Families seeking further information may contact Medinfo@Shionogi.com or (800) 849-9707, or reach out to FRAXA Research Foundation for additional support and resources.
