Intellia Therapeutics halted enrollment and dosing in two Phase III trials of its in vivo CRISPR candidate after a trial participant developed severe liver injury requiring hospitalization. The affected program, nexiguran ziclumeran (nex‑z), is aimed at transthyretin amyloidosis (ATTR); Intellia said it is pausing to investigate the event and implement revised safety monitoring. The company notified investigators and regulators and is evaluating dosing and monitoring protocols while clinical sites suspend new dosing. Intellia emphasized an abundance-of-caution approach as it probes on-target versus off-target mechanisms of hepatotoxicity. Market reaction was swift: the news pressured Intellia’s valuation and raises broader questions about safety margins for systemic, one‑time CRISPR editing approaches. The pause will likely delay regulatory timelines and could reshape risk frameworks for other in vivo gene‑editing programs, prompting sponsors and regulators to reassess monitoring, biomarker strategies and enrollment criteria for high‑impact editing medicines.