Ultragenyx Pharmaceutical and Mereo BioPharma disclosed that late-stage trials of setrusumab failed to meet primary endpoints, prompting a sharp market reaction. Mereo’s stock plunged roughly 90% on the announcement and Ultragenyx shares also dropped as both firms said they are reviewing the data and next steps. The failures remove a late-stage candidate for osteogenesis imperfecta and force reassessment of commercial and clinical strategies.