Ultragenyx's gene therapy helps control ammonia levels in late-stage study

March 12 (Reuters) - Ultragenyx Pharmaceutical RARE.O said on Thursday its experimental gene therapy helped patients in a late-stage trial to better control ammonia levels linked to a rare inherited disorder.

The therapy, called DTX301, improved a key measure of ammonia control by 18% after 36 weeks in patients with ornithine transcarbamylase, or OTC deficiency, compared with a placebo, the company said.

Shares of the company were up 3.5% following the news.

OTC deficiency is a rare inherited disorder caused by the lack of a liver enzyme that helps clear ammonia, leading to a toxic buildup that can trigger confusion, seizures and coma.

Most patients who started the study with abnormal ammonia levels reached normal levels quickly and generally stayed there through the 36-week period, Ultragenyx said.

The company also said treated patients were able to cut back on ammonia-lowering medicines and eat 13% more protein while keeping ammonia under control.

The placebo group recorded five hospitalizations tied to dangerous ammonia spikes, including one death, compared with one such hospitalization and no deaths among the treated patients, Ultragenyx said.

The company said the drug was generally well tolerated. The most common side effects were liver-related problems that were managed with steroids.

Ultragenyx said the trial will continue to its second study goal, which will evaluate if DTX301 can reduce treatment burden, including the need for ammonia-lowering drugs and dietary restrictions.

The company expects those data in the first half of 2027.