The U.S. Food and Drug Administration has imposed a clinical hold on Intellia Therapeutics’ two Phase 3 studies of nexiguran ziclumeran (nex‑z), a CRISPR‑based in vivo genome‑editing therapy for transthyretin amyloidosis, after reports of liver complications. Intellia paused dosing and notified investigators as regulators and the company review safety data to determine causality and next steps. Nex‑z uses CRISPR to inactivate the gene producing the pathogenic protein; the hold highlights the regulatory scrutiny around systemic in vivo gene editors and reinforces the agency’s focus on off‑target or organ‑specific toxicities. Sponsors, investigators and contract manufacturers will need to provide additional safety analyses and risk‑mitigation plans before the studies can resume. The decision is likely to affect timelines for other in vivo editing programs and could prompt sponsors to tighten monitoring protocols and preclinical liver‑toxicity assays. Investors and trial sites should expect updates as Intellia engages with the FDA to resolve the hold.