Ultragenyx reported that its gene therapy candidate achieved one of two primary endpoints in a Phase 3 trial for ornithine transcarbamylase (OTC) deficiency, a rare urea cycle disorder. The multicenter study enrolled 37 patients, and the company said hitting a primary endpoint supports the therapy’s biological effect in correcting ammonia control. The partial success nevertheless leaves a second co‑primary endpoint unmet or pending, and Ultragenyx will work with regulators to define the path to approval. The result provides a pivotal efficacy signal for a genetically targeted treatment in a small, heterogeneous patient population. Investors and rare‑disease stakeholders will watch follow‑up analyses and regulatory interactions closely; the readout illustrates the complexity of designing co‑primary endpoints for gene therapies in metabolic diseases where clinical benefit can be multifactorial.