An elderly patient dosed with Intellia and Regeneron’s in‑vivo CRISPR candidate nexiguran ziclumeran (nex‑z) died after developing severe liver dysfunction, prompting sponsors and the FDA to pause dosing and screening in large Phase III MAGNITUDE studies. Intellia disclosed Grade 4 transaminase elevations and rising bilirubin in the hospitalized patient and said it is working with investigators and external experts to investigate the signal and develop risk‑mitigation strategies. The FDA moved quickly to impose a clinical hold on the INDs covering the MAGNITUDE trials while reviewing the events; Intellia has mandated enhanced early post‑dose lab monitoring at sites. Company statements note comorbidities in the patient and cite a very low incidence of comparable Grade 4 events across enrolled patients, but investors have reacted sharply and the hold raises broader questions about safety for LNP‑delivered CRISPR therapies. Sponsors plan systematic case reviews, additional lab collection and potential exclusion criteria to identify at‑risk patients. Regulators and competitors will be watching whether the events represent a therapy‑specific toxicity, a delivery‑related effect, or patient selection issues — a distinction that will shape the path for in‑vivo gene editing programs.