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Transthyretin amyloidosis with cardiomyopathy (ATTR-CM) is a progressive, often fatal disease. Nexiguran ziclumeran (nex-z) is an investigational therapy based on CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats and associated Cas9 endonuclease) targeting the gene encoding transthyretin ( ). In this phase 1, open-label trial, we administered a single intravenous infusion of nex-z to patients with ATTR-CM. Primary objectives included assessment of the effect of nex-z on safety and pharmacodynamics, including the serum TTR level. Secondary end points included changes in N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels, high-sensitivity cardiac troponin T levels, the 6-minute walk distance, and the New York Heart Association (NYHA) class. A total of 36 patients received nex-z and completed at least 12 months of follow-up. Of these patients, 50% were in NYHA class III and 31% had variant ATTR-CM. The mean percent change from baseline in the serum TTR level was -89% (95% confidence interval [CI], -92 to -87) at 28 days and -90% (95% CI, -93 to -87) at 12 months. Adverse events were reported in 34 patients. Five had transient infusion-related reactions, and two had transient liver-enzyme elevations that were assessed as treatment-related. Serious adverse events, most of which were consistent with ATTR-CM, were reported in 14 patients. The geometric mean factor change from baseline to month 12 was 1.02 (95% CI, 0.88 to 1.17) in the NT-proBNP level and 0.95 (95% CI, 0.89 to 1.01) in the high-sensitivity cardiac troponin T level. The median change from baseline to month 12 in the 6-minute walk distance was 5 m (interquartile range, -33 to 49). A total of 92% of the patients had either improvement or no change in their NYHA class. In this phase 1 study involving patients with ATTR-CM, treatment with a single dose of nex-z was associated with transient infusion-related reactions and consistent, rapid, and durable reductions in serum TTR levels. (Funded by Intellia Therapeutics and Regeneron Pharmaceuticals; ClinicalTrials.gov number, NCT04601051.).

Hereditary transthyretin amyloidosis with polyneuropathy (ATTRv-PN) is a rare, multisystem, progressive, debilitating, and fatal disease characterized by tissue deposition of misfolded transthyretin (TTR) in peripheral nerves. Nexiguran ziclumeran (nex-z) is an investigational in vivo therapy based on CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats and associated Cas9 endonuclease) that is designed to reduce serum TTR levels through selective inactivation of in the liver. In this phase 1, open-label study, we administered one infusion of nex-z to patients with ATTRv-PN. Primary objectives included assessment of the safety and pharmacodynamics of nex-z. Secondary end points included changes in the familial amyloid polyneuropathy stage, polyneuropathy disability score, serum neurofilament light chain (NfL) level, modified body-mass index (modified BMI, defined as the conventional BMI [weight in kilograms divided by square of height in meters] multiplied by the albumin level in grams per liter), and modified Neuropathy Impairment Score+7 (mNIS+7; range, 0 to 304, with higher scores indicating more impairment). A total of 36 patients received nex-z; the mean follow-up was 27 months. The mean percent change from baseline in the serum TTR level was -90% at day 28, which was sustained through month 24 (-92%). Treatment-related adverse events included transient infusion-related reactions (in 21 patients), decreased thyroxine level without hypothyroidism or elevated thyrotropin level (in 8), and headache (in 4). One participant died from cardiac amyloidosis, and one withdrew owing to progressive decline in motor function. Serious adverse events were reported in 11 patients. At month 24, the familial amyloid polyneuropathy stage and polyneuropathy disability score remained stable in 29 and 27 patients, respectively; improved in 2 and 5, respectively; and worsened in 2 and 2, respectively. The mean change in the serum NfL level was -9.0 pg per milliliter, and the change in the modified BMI was 24.7. The mean change from baseline in the mNIS+7 was -8.5. A single administration of nex-z in patients with ATTRv-PN was associated with rapid, deep, and durable reductions in serum TTR levels. The results support further investigation of nex-z to treat ATTRv-PN. (Funded by Intellia Therapeutics and Regeneron Pharmaceuticals; ClinicalTrials.gov number, NCT04601051.).