An Extension Study to Assess Long-Term Safety of Eplontersen in Adults With Transthyretin-Mediated Amyloid Cardiomyopathy (ATTR-CM)

The purpose of this study is to evaluate the safety and tolerability of extended dosing with eplontersen in participants with ATTR-CM.

This is a multicenter, open-label extension, Phase 3 study in up to approximately 1400 participants from the 682884-CS2 study. Eligible participants will receive eplontersen once every 4 weeks for up to 36 months or until after eplontersen is approved and available in the site's country, whichever occurs first. Participants will also receive daily supplemental doses of the recommended daily allowance (RDA) of vitamin A.

Inclusion Criteria: 1. Satisfactory completion of Treatment Period and the End of Treatment Visit of the Index Study (ION-682884-CS2) OR diagnosis of ATTR-CM and satisfactory participation on ISIS 420915- CS101 study as judged by the Investigator and Sponsor. 2. Investigator is willing to treat the participant with open-label eplontersen. 3. Willingness to adhere to vitamin A supplementation per protocol. Exclusion Criteria: 1. Permanently discontinued study drug administration while participating in the Index Study (ION 682884-CS2) or IST (ISIS 420915-CS101 Study). 2. Have any new condition or worsening of an existing condition that in the opinion of the Investigator or Sponsor would make the participant unsuitable for enrolment, or which could interfere with the participant participating in or completing the study, including the need for treatment with medications disallowed in the Index Study.