The U.S. Food and Drug Administration placed a clinical hold on two late-stage Phase 3 trials of Intellia Therapeutics’ CRISPR candidate nexiguran ziclumeran (nex‑z) after a Grade 4 liver adverse event hospitalized a participant. Intellia had already paused dosing voluntarily and notified investors; the formal FDA hold raises the regulatory bar and pauses patient enrolment. The agency will issue a formal letter within 30 days outlining required information; Intellia must respond and satisfy FDA requests before dosing can resume. The company is working with independent experts to revise safety monitoring and risk‑mitigation strategies. Nex‑z targets transthyretin amyloidosis (ATTR), a hereditary protein‑misfolding disease. A clinical hold on gene‑editing programs typically triggers extended timelines, additional monitoring requirements, and heightened scrutiny of preclinical and clinical safety data.