A Study to Assess the Long-Term Safety and Efficacy of Eplontersen (Formerly Known as ION-682884, IONIS-TTR-LRx and AKCEA-TTR-LRx) in Patients With Hereditary Transthyretin-Mediated Amyloid Polyneuropathy

Inclusion Criteria:

1. Satisfactory completion of ION-682884-CS3 (NCT04136184) (Index Study) as judged bythe Investigator and Sponsor, or diagnosis of hATTR-PN and satisfactory completionof either study ISIS 420915-CS101 or study 2018-P001436 (NCT03702829) (both areInvestigator-Sponsored studies with inotersen - the unconjugated version ofeplontersen) as judged by the Investigator and Sponsor.

2. Must have given written informed consent (signed and dated) and any authorizationsrequired by local law and be able to comply with all study requirements.

3. Satisfy the following:

4. Females: must be non-pregnant and non-lactating and either:

• Surgically sterile (e.g., tubal occlusion, hysterectomy, bilateralsalpingectomy, bilateral oophorectomy);
• Post-menopausal (defined as 12 months of spontaneous amenorrhea in females > 55 years of age or, in females ≤ 55 years, 12 months of spontaneousamenorrhea without an alternative medical cause and follicle-stimulatinghormone (FSH) levels in the postmenopausal range for the laboratoryinvolved;
• Abstinent*;
• If engaged in sexual relations of child-bearing potential, agree to usehighly effective contraceptive methods from the time of signing theinformed consent form until at least 24 weeks after the last dose ofeplontersen and agree to receive pregnancy tests per protocol.

2. Males: Surgically sterile (i.e., bilateral orchidectomy) or abstinent*, ifengaged in sexual relations with a woman of child-bearing potential (WOCBP),the participant or the participant's non-pregnant female partner must use ahighly effective contraceptive method from the time of signing the informedconsent form until at least 24 weeks after the last dose of eplontersen. *Abstinence (i.e., refraining from heterosexual intercourse throughout theduration of study participation) is only acceptable as true abstinence, i.e.,when this is in line with the preferred and usual lifestyle of the participant.Periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulationmethods), declaration of abstinence for the duration of a trial and withdrawalare not acceptable methods of contraception.

3. Willingness to adhere to vitamin A supplementation per protocol.

Exclusion Criteria:

1. Have any new condition or worsening of existing condition that in the opinion of the Investigator or Sponsor would make the participant unsuitable for enrollment or could interfere with the participant taking part in or completing the study.