Late‑stage trials of setrusumab, an antibody intended to treat brittle‑bone disease (osteogenesis imperfecta), failed to meet primary endpoints, sending Ultragenyx and Mereo shares sharply lower and prompting strategic reassessments. The Phase III misses leave the program’s developers scrambling to interpret secondary endpoint signals and consider next steps, including potential portfolio restructuring or company wind‑down options. The outcome highlights the clinical and commercial risks of late‑stage rare‑disease programs and the market sensitivity to pivotal readouts. Investors and companies will be watching how sponsors reallocate resources and whether data subanalyses yield salvageable regulatory or commercial strategies.