09:11 AM EST, 12/29/2025 (MT Newswires) -- Ultragenyx Pharmaceutical ( RARE ) said Monday that 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 Pharmaceutical ( RARE ) shares were down 43% in recent premarket trading, following a trading halt.