Participants with documented homozygous familial hypercholesterolemia (HoFH) who have provided informed consent will receive 2 open-label doses of ARO-ANG3 and be evaluated for safety and efficacy parameters through 36 weeks. Participants who complete the first 36 week treatment period may opt to continue in an additional 24-month extension period during which they will receive up to 8 doses open-label doses of ARO-ANG3.