The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of single- and multiple doses of ARO-APOC3 in healthy adult volunteers and in patients with severe hypertriglyceridemia and familial chylomicronemia syndrome (FCS).

Inclusion Criteria:

• 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
• Normal electrocardiogram (ECG) at screening
• Hypertriglyceridemic patients must have a history of fasting serum triglycerides of at least 300 mg/dL (3.38 mmol/L) at screening or verifiable diagnosis of FCS

Exclusion Criteria:

• Clinically significant health concerns
• Regular use of alcohol within one month prior to Screening
• Use of an investigational agent or device within 30 days prior to dosing or current participation in an investigational study
• Recent use of illicit drugs
• Use of more than two tobacco/nicotine containing or cannabis products per month within 6 months prior to drug administration (applicable only to Normal Healthy Volunteers)

Note: additional inclusion/exclusion criteria may apply, per protocol