The FDA placed a clinical hold on two Phase 3 trials of Intellia Therapeutics’ CRISPR candidate nexiguran ziclumeran after a participant experienced severe liver enzyme elevations and hospitalization. Intellia had already paused dosing voluntarily and notified regulators; the FDA’s formal hold requires a written agency response and a company plan before trials can resume. Intellia is working with external experts and the agency to analyze safety signals and propose additional monitoring and mitigation steps. The pause affects studies in transthyretin amyloidosis—an indication where Intellia positioned its in vivo CRISPR approach as a long-acting alternative to current therapies. Regulatory scrutiny now adds months of uncertainty to a program that had reached late-stage testing and large enrollment, and the hold will shape investor and competitor responses across in vivo gene-editing pipelines.