Inclusion Criteria: 

• Male and female participants starting at birth.
• Diagnosis of PH3 confirmed by genotyping (historically available genotype information is acceptable for study eligibility).
• For participants at least 2 years of age, history of stone events during the last 3 years and/or presence of preexisting stones detected by renal ultrasound at Screening.
• 24-hour Uox ≥ 0.7 mmol (adjusted per 1.73 m^2 BSA in participants < 18 years of age) on each of the 2 collections during Screening; OR If not able to collect 24-hour urine, average spot Uox to creatinine ratio at Screening above the 95th percentile for age (Matos et al, 1990):
  • > 220 mmol/mol in participants < 6 months;
  • > 170 mmol/mol in participants from 6 months to < 12 months;
  • > 130 mmol/mol in participants 12 months to < 2 years;
  • > 100 mmol/mol in participants from 2 to < 3 years; and
  • > 80 mmol/mol in participants from 3 to 5 years.
• If able to collect 24-hour urine, less than 20% variation between the two 24-hour urinary creatinine measurements in the Screening period. Individuals who do not achieve < 20% variation between the 2 Screening values may undergo a second round of urine collection. An extra 14 calendar days may be added to the Screening window for participants to complete a second round of urine collection. Should potential participants again fail to achieve < 20% variation, they will be excluded from participation.
• Estimated GFR at Screening ≥ 30 mL/min/1.73 m^2, calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation in participants aged ≥ 18 years (Levey & Stevens, 2010), or the multivariate equation by Schwartz in participants aged 12 months to 17 years (Schwartz et al., 2012); OR For infants aged less than 12 months, serum creatinine below the 97th percentile of a healthy population (Boer et al., 2010).
• Body weight ≥ 5.7 kg.
• Participant (and/or participant’s parent or legal guardian if participant is a minor [defined as patient < 18 years of age, or younger than the age of majority, according to local regulations]) is capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the ICF and in this protocol:
  • Adolescents (12 to < 18 years of age, or older than 12 years but younger than the age of majority, according to local regulations) must be able to provide written assent for participation;
  • For children younger than 12 years of age, assent will be based on local regulations.

Exclusion Criteria:  

• Prior hepatic transplantation; or planned transplantation within the study period.
• Currently receiving dialysis or anticipating requirement for dialysis during the study period.
• Inability or unwillingness to comply with the specified study procedures.

Eligibility last updated 9/14/21. Questions regarding updates should be directed to the study team contact.