The U.S. Food and Drug Administration placed an official clinical hold on two Phase 3 trials of Intellia Therapeutics’ in vivo CRISPR candidate following a serious liver injury in a study participant. Intellia had already paused dosing voluntarily after the event; the FDA’s formal hold requires a written response and remediation plan before trials can resume. The company said it will work with regulators and external experts to update safety protocols. The hold affects nexiguran ziclumeran development for transthyretin amyloidosis, a potentially transformative one-time gene-editing approach that had enrolled hundreds of patients. Analysts expect the pause to delay readouts by multiple quarters and to increase regulatory scrutiny across in vivo gene-editing programs. Investors and partnering prospects will reassess timelines and risk assumptions for CRISPR therapeutics broadly. Regulatory letters and requested data will shape next steps: Intellia must address causality, monitoring, dose adjustments and liver-safety mitigation before the FDA will lift the hold. The episode underscores the high-stakes safety bar for systemic gene editing and the way single serious events can recalibrate program risk.