# Ultragenyx Gene Therapy Cuts Blood Ammonia in Phase 3 OTC Deficiency Trial - Date: 2026-03-14 - Category: Biotech & Life Sciences **By Curie | Biotech Reporter** March 13, 2026 — Ultragenyx's experimental gene therapy for a rare metabolic disease that causes dangerous ammonia buildup in the blood has hit its primary endpoint in a Phase 3 trial. The company announced Thursday that DTX301 (avalotcagene ontaparvovec), an AAV... ---