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Ultragenyx Announces Positive 36-Week Data from Phase 3 Study of DTX301 AAV8 Gene Therapy for the Treatment of Ornithine Transcarbamylase (OTC) Deficiency
Statistically significant improvements in primary endpoint of ammonia control compared with placebo at 36 weeks Clinically important changes observed in
About this update from Ultragenyx Pharmaceutical Inc.
[{"type":"text","content":"Statistically significant improvements in primary endpoint of ammonia control compared with placebo at 36 weeks Clinically important changes observed in patient global impression scale for overall OTC symptoms, OTC deficiency symptoms, and OTC impact on daily living DTX301 was well tolerated with an acceptable safety profile NOVATO, Calif., March 12, 2026 (GLOBE NEWSWIRE) -- Today Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) announced positive results from its Phase 3 Enh3ance study of DTX301, an investigational AAV8 gene therapy for the treatment of ornithine transcarbamylase (OTC) deficiency. At Week 36 in the randomized, double-blind placebo-controlled period of the trial, DTX301-treated patients (n=18) demonstrated a statistically significant and clinically meaningful 18% (p=0.018) reduction in 24-hour plasma ammonia (AUC0-24) compared to placebo (n=19) and maintained average ammonia AUC0-24 in the normal range through Week 36. Eight of nine patients with abnormal ammonia AUC0-24 at baseline, despite optimal current drug treatment and diet restriction, reached normal ammonia levels rapidly, which were generally maintained during this treatment period. “Given the importance of and effort made to keep ammonia levels under control in patients with OTC deficiency, the further reduction in ammonia levels in patients treated with DTX301 demonstrates the benefit of this gene therapy and of directly addressing the underlying cause of this disease,” said Eric Crombez, M.D. chief medical officer of Ultragenyx. “Importantly, the improvement in ammonia control was maintained as some patients began reducing use of alternate pathway medications and liberalizing their protein restricted diet. We are extremely encouraged by these findings given the significant medical needs faced by patients with OTC deficiency, who remain at risk for unpredictable and potentially life threatening hyperammonemic crises.” Baseline 24-hour ammonia AUC levels were normal in 50% of DTX301-treated patients and 68% of placebo patients, who were all on current care of scavenger medications and strict dietary control of protein intake. Patients treated with DTX301 (n=18) experienced reductions in 24-hour ammonia rapidly by Week 6 and were decreased by 18% (p=0.018) compared to placebo (n=19) at Week 36. Ammonia was generally maintained in normal range in treated p...