Study to Evaluate Safety, Tolerability, PK and PD of DCR-PHXC in PH Type 3 Patients

Key Inclusion Criteria: * Genetically confirmed PH3 * 24-hour Uox excretion ≥ 0.7 mmol (adjusted per 1.73 m\^2 body surface area \[BSA\] in participants \< 18 years of age) on both assessments conducted in the screening period * Less than 20% variation between the two 24-hour urinary creatinine excretion values (mmol/kg/24 hours) in the screening period * Estimated glomerular filtration rate (eGFR) at screening ≥ 30 mL/min, normalized to 1.73 m\^2 BSA * History of at least one stone event within the last 12 months. Stone events are defined as any of the following: * renal stone requiring medical intervention, e.g., outpatient procedures such as lithotripsy, or hospitalization or inpatient surgical intervention for confirmed stone-related pain and/or complications; * stone passage with or without hematuria; or * renal colic requiring medication. Key Exclusion Criteria: * Documented evidence of clinical manifestations of systemic oxalosis (including pre-existing retinal, heart, or skin calcifications, or history of severe bone pain, pathological fractures, or bone deformations) * Plasma oxalate \> 30 μmol/L