Long Term Extension Study in Patients With Primary Hyperoxaluria

The proposed study is designed to provide patients previously enrolled in Phase 1 and 2 studies of DCR-PHXC and their siblings (\<18 years old) long-term access to DCR-PHXC, and to evaluate the long-term safety and efficacy of DCR-PHXC in patients with PH.

Key Inclusion Criteria: •Participant successfully completed a Dicerna Pharmaceuticals, Inc. study of DCR PHXC. OR Participant is the sibling of a participant who successfully completed a Dicerna Pharmaceuticals, Inc. study of DCR PHXC. Siblings must be younger than 18 years of age and must have genetically confirmed PH. * For participants rolling over from a multidose study of DCR-PHXC, enrollment should occur within a window of 25 to 75 days from the last dose of study intervention. * Estimated GFR at screening ≥ 30 mL/min normalized to 1.73 m2 body surface area (BSA), calculated using Chronic Kidney Disease Epidemiology Collaboration (CKD EPI) formula in participants aged ≥ 18 years, or the multivariate equation by Schwartz in participants aged 12 months to 17 years. In Japan, the cystatin C-based Uemura formula will be used for participants aged 12 months to \<2 years, the creatinine-based Uemura formula by will be used for participants aged 2 to 17 years, and the equation by Matsuo will be used in participants aged ≥ 18 years. Key Exclusion Criteria: * Renal or hepatic transplantation (prior or planned within the study period) * Plasma oxalate \> 30 µmol/L * Currently on dialysis * Documented evidence of clinical manifestations of systemic oxalosis