Ultragenyx reported that its gene therapy candidate achieved one of two co‑primary endpoints in a Phase‑3 study for ornithine transcarbamylase (OTC) deficiency, a rare urea‑cycle disorder that causes toxic ammonia buildup. The readout comes from a 37‑patient study and marks a critical efficacy milestone for the program as the company advances toward potential regulatory filings. The trial’s success on a primary biochemical endpoint—reduction of blood ammonia—supports the therapy’s proposed mechanism and could underpin efficacy claims in regulatory submissions for this life‑threatening metabolic disease. Ultragenyx positioned the data as a key validation step for its rare‑disease gene‑therapy portfolio. Sponsors and regulators typically seek functional and safety outcomes alongside biochemical improvements; further results and regulatory interactions will determine the path to approval and commercial access for patients with OTC deficiency.