The purpose of this study is to evaluate the safety and tolerability of olezarsen in participants with SHTG.

This is a multi-center, open-label extension (OLE) study of approximately 800 participants with SHTG who would be rolled over from studies ISIS 678354-CS5 (NCT05079919) or ISIS 678354-CS6 (NCT05552326). Day 1 of this study may be same as the Week 53 visit of either ISIS 678354-CS5 or ISIS 678354-CS6, as applicable. Participants will receive olezarsen during the 157-week treatment period. The study will include a 31-day qualification Period, a 157-week treatment period, and a 13-week post-treatment period.

Key Inclusion Criteria:

• Satisfactory completion of either ISIS 678354-CS5 or ISIS 678354-CS6 with an acceptable safety profile, per Investigator judgment. Satisfactory completion requires that the patient did not terminate early from treatment.
• Participants must be on a stable regimen of lipid-lowering therapy that should adhere to standard of care (SOC) per local guidelines. A patient may be eligible if their regimen of lipid-lowering therapy has been changed recently, provided that lipid lowering medications are optimized and stabilized for at least 4 weeks prior to the end of the Qualification Period of this OLE study; ideally, such changes are initiated after Week 53 of the index study (ISIS 678354-CS5 or CS6).
• A patient may re-enroll in the study after having completed the study when the Treatment Period was 53 weeks, if the patient satisfactorily completed the study with an acceptable safety profile, per Investigator judgment. In the case of re-enrollment, there is no limit on the time gap between completion of treatment under the previous protocol and dosing upon re-enrollment (i.e., may exceed 17 weeks between doses).

Key Exclusion Criteria:

• Have any new condition or worsening of existing condition which in the opinion of the Investigator would make the participant unsuitable for enrollment, or could interfere with the participant participating in or completing the study, including need for treatment with disallowed medications, or need to change the required stable regimen as per either ISIS 678354-CS5 or ISIS 678354-CS6 study entry criteria. It is acceptable to adjust a regimen of lipid-lowering therapy as described in the second Key Inclusion Criterion above, and it is acceptable to adjust or stop lipid-lowering therapy at or after Week 13 per Investigator judgment.

NOTE: Other Inclusion/Exclusion criteria may apply.

Ionis may share anonymized individual participant data, aggregated clinical data, and other types of data that support the results in this study. Data requests from qualified researchers will be considered once all three of the following criteria are met: (1) 12 months from marketing approval of the study drug in both the United States and European Union; (2) 18 months from conclusion of the study; and (3) 6 months from publication of study article. Access would be via a secure environment and is contingent upon approval of a research proposal and entry into an appropriate data use agreement. Requests to access data can be submitted via the website https://vivli.org/ourmember/ionis/.