The FDA placed a formal clinical hold on two Phase 3 trials of Intellia Therapeutics’ CRISPR candidate nexiguran ziclumeran after a Grade 4 liver‑toxicity event prompted the company to pause dosing. Intellia had already stopped enrollment and dosing voluntarily; the agency will issue a formal hold letter within 30 days and request responses before trials can resume. Intellia is developing nex‑z for transthyretin amyloidosis (cardiomyopathy and polyneuropathy forms). The company had enrolled hundreds of patients across the two studies; analysts now expect several‑quarter delays to readouts while sponsors and regulators define additional safety monitoring and mitigation steps. "Grade 4" refers to life‑threatening laboratory abnormalities that require hospitalization or urgent intervention. The hold refocuses attention on on‑target and organ‑specific risks for systemically delivered in vivo gene‑editing therapies and raises scrutiny across CRISPR clinical programs. Investors and partners are watching how Intellia and the FDA align on revised inclusion criteria, monitoring, and stopping rules before dosing can restart.