Ultragenyx Pharmaceutical Inc. announced topline positive safety and efficacy data from Cohort 3 and longer-term data from Cohort 2 of the ongoing Phase 1/2 study of DTX301, an investigational adeno-associated virus (AAV) gene therapy for the treatment of ornithine transcarbamylase (OTC) deficiency. In Cohort 3 (n=3), there were two confirmed female responders as well a third potential male responder who requires longer-term follow-up to confirm response status. In Cohort 2, one female patient has newly demonstrated a response starting at Week 52 which was confirmed at Week 78. The two previously disclosed responders in Cohort 1 and Cohort 2 also remain clinically and metabolically stable at 104 and 78 weeks, respectively. Across all nine patients dosed in the study, up to six patients have demonstrated a response.