Intellia reported that an elderly patient dosed with its in‑vivo CRISPR candidate nexiguran ziclumeran (nex‑z) died after hospitalization for severe liver injury, and the FDA placed a clinical hold on the MAGNITUDE Phase 3 studies. The company paused dosing and screening across the two trials while it investigates elevated transaminases and develops risk‑mitigation measures. Intellia and partner Regeneron disclosed the event after first reporting a Grade 4 hepatic signal in late October; company executives said the case involved complicating comorbidities and emphasized the overall low frequency of similar events across more than 650 ATTR‑CM patients enrolled. The FDA’s hold freezes further enrollment and dosing pending agency review and a formal clinical‑hold letter. Investors reacted sharply: Intellia shares collapsed following the disclosure, and market observers noted the event complicates commercialization timelines for a one‑time in vivo CRISPR therapy that had shown promising early durability. Intellia said it is working with clinical sites and external experts to refine monitoring and exclusion criteria and will await the FDA’s formal guidance. For developers of systemic gene editing and LNP‑delivered therapies, the case highlights immediate regulatory sensitivity around off‑target or treatment‑related organ toxicity and the need for detailed hepatic safety strategies in large, single‑dose programs.