Study to Evaluate ARO-APOC3 in Adults With Severe Hypertriglyceridemia

Inclusion Criteria: * Based on medical history, evidence of triglycerides (TG) ≥ 500 mg/dL and ≤ 4000 mg/dL at Screening * Fasting TG ≥ 500 mg/dL at Screening * Willing to follow diet counseling per Investigator judgment based on local standard of care * Women of childbearing potential must have a negative pregnancy test, cannot be breastfeeding, and must be willing to use contraception * Willing to provide written informed consent and to comply with study requirements Exclusion Criteria: * Active pancreatitis within 12 weeks prior to first dose * Any planned bariatric surgery or similar procedures to induce weight loss from consent to end of study * Acute coronary syndrome event within 24 weeks of first dose * Major surgery within 12 weeks of first dose * Planned coronary intervention (e.g., stent placement or heart bypass) or any non-cardiac major surgical procedure throughout the study * Uncontrolled hypertension * Human immunodeficiency virus (HIV) infection, seropositive for Hepatitis B (HBV), seropositive for Hepatitis C (HCV) * Uncontrolled hypothyroidism or hyperthyroidism * Hemorrhagic stroke within 24 weeks of first dose * Malignancy within the last 2 years prior to date of consent requiring systemic treatment (some exceptions apply) Note: additional inclusion/exclusion criteria may apply per protocol