Study Overview: This research is testing a new injection called plozasiran (ARO-APOC3) to see if it helps adults with severe hypertriglyceridemia (SHTG). SHTG means having very high levels of triglycerides, which are a type of fat in your blood. The study will check how safe and effective plozasiran is. Participants will get four injections, one every three months, and their health will be checked along the way. After one year, participants can choose to continue in another part of the study.

Eligibility: To join, you need to have high triglyceride levels (≥ 500 mg/dL) and be willing to follow a low-fat diet. You should also be on medication for managing fats in your blood unless you can't tolerate them. You cannot join if you have used certain medications or have certain conditions like acute pancreatitis or a very high body mass index.

• The study lasts for at least one year.
• Participants will receive four injections and regular health checks.
• There is an option to continue after the first year.