Ultragenyx Pharmaceutical said it will look to reduce expenses and evaluate its development of apazunersen after the drug failed to meet its primary endpoint in a Phase 3 trial.

The treatment didn't meet the primary endpoint of improving cognitive scores in patients with Angelman syndrome, a rare neuro-genetic disease, the company said. The drug also missed the study's secondary endpoint.

Based on the results, Ultragenyx said it will evaluate the apazunersen program and make a decision on its future. It said it will also "assess its planned operations to define and implement significant expense reductions, while supporting its growing commercial business."

Shares plunged on the news, trading down 45% at $14.65 after Wednesday's bell.

"Based on everything we observed in the robust Phase 1/2 clinical development program and long-term extension study, we are disappointed by the Aspire result," Chief Executive Emil Kakkis said.

He added that the company will focus on expanding its existing commercial business, including into new markets, as it looks to reach profitability next year.