Core Viewpoint - A class action has been filed against Ultragenyx Pharmaceutical Inc. for allegedly misleading investors regarding the efficacy of setrusumab in clinical studies, leading to significant stock price decline after the announcement of study failures [1][4]. Group 1: Allegations and Misleading Information - Robbins LLP is investigating allegations that Ultragenyx misled investors about the expected results of its Phase III Orbit and Cosmic Studies for setrusumab, claiming it would reduce fracture rates in Osteogenesis Imperfecta patients [2]. - The complaint asserts that Ultragenyx provided overly positive statements while concealing material adverse facts about setrusumab's potential and the risks associated with the study protocols, particularly that increased bone density did not correlate with reduced fracture rates [3]. Group 2: Study Results and Stock Impact - On December 29, 2025, Ultragenyx announced that its Phase III studies did not achieve statistical significance in reducing annualized clinical fracture rates compared to placebo or bisphosphonates, attributing the failure to a low fracture rate in the placebo group [4]. - Following this announcement, Ultragenyx's stock price plummeted from $34.19 per share on December 26, 2025, to $19.72 per share on December 29, 2025, marking a decline of approximately 42.32% in one day [4].