An elderly patient treated with Intellia Therapeutics’ in vivo CRISPR therapy nexiguran ziclumeran (nex‑z) died after severe liver injury, triggering FDA clinical holds on the company’s Phase 3 MAGNITUDE and MAGNITUDE‑2 trials. Intellia said the patient, described as an early‑80s man with complicating comorbidities, presented Grade 4 transaminase elevations and increased bilirubin several weeks after dosing. Intellia notified sites and elevated monitoring for early liver‑lab abnormalities while working with clinical investigators and external experts to investigate the signal and develop risk‑mitigation steps. The company and Regeneron, its collaborator on nex‑z, stressed that Grade 4 enzyme elevations have occurred in fewer than 1% of the >650 MAGNITUDE enrollees. Regulatory action followed quickly: the FDA placed the trials on clinical hold pending a formal letter. Investors sold off shares across the gene‑editing supply chain on the news, underscoring how a single severe adverse event can reshape development timelines for in‑vivo genome editors. The agency and company said further details are under investigation.