09:57 AM EST, 12/29/2025 (MT Newswires) -- (Updates with recent stock price movement in the headline and first paragraph, and adding information on partnership with Mereo in the fifth paragraph.)

Ultragenyx Pharmaceutical's ( RARE ) shares fell more than 45% in recent Monday trading after the company said its phase 3 studies of setrusumab to treat osteogenesis imperfecta, or brittle bone disease, did not achieve the primary endpoints of reduction in annualized clinical fracture rate compared to placebo or bisphosphonates.

Both studies achieved the secondary endpoints of improvements in bone mineral density against comparators, the company said.

Ultragenyx said it is conducting additional analyses across both studies to evaluate its next steps.

The company said it also assessing its planned operations and will implement "significant" expense reductions.

Ultragenyx said it is developing setrusumab in pediatric and young adult patients with osteogenesis imperfecta in partnership with Mereo BioPharma ( MREO ) . Shares of Mereo were down more than 89% in recent trading Monday.

Price: 18.78, Change: -15.42, Percent Change: -45.09