Study of Sparsentan in Patients With Primary Focal Segmental Glomerulosclerosis (FSGS)

Key Inclusion Criteria for the Double-blind Period: * Sites within the US and UK: The patient is male or female aged 8 to 75 years, inclusive, weighing ≥20 kg at screening * Sites outside the US and UK: The patient is male or female aged 18 to 75 years, inclusive, weighing ≥20 kg at screening * Biopsy-proven focal segmental glomerulosclerosis (FSGS) lesion(s) or documentation of a genetic mutation in a podocyte protein associated with FSGS. * Urine protein/creatinine (UP/C) ≥1.5 g/g (170 mg/mmol) at screening * eGFR ≥30 mL/min/1.73 m2 at screening. * Women of childbearing potential must agree to the use of one highly reliable method of contraception from 7 days prior to the first dose of study medication until 90 days after the last dose of study medication, plus one additional barrier method during sexual activity Key Exclusion Criteria for the Double-blind Period: * FSGS secondary to another condition * Positive serological tests of another primary or secondary glomerular disease not consistent with a diagnosis of primary or genetic FSGS * History of type 1 diabetes mellitus, uncontrolled type 2 diabetes mellitus, or nonfasting blood glucose \>180 mg/dL (10.0 mmol/L) * Treated with rituximab, cyclophosphamide, or abatacept within ≤3 months prior to screening; if taking other chronic immunosuppressive medications, the dosage must be stable prior to screening * Documented history of heart failure, coronary artery disease, or cerebrovascular disease * Significant liver disease * Positive at screening for the human immunodeficiency virus or markers indicating acute or chronic hepatitis B virus infection or hepatitis C infection * History of malignancy other than adequately treated basal cell or squamous cell skin cancer or cervical carcinoma within the past 2 years * Screening hematocrit value \<27% (0.27 L/L) or hemoglobin value \<9 g/dL (90 g/L) * Screening potassium value of \>5.5 mEq/L (5.5 mmol/L) * Extreme obesity (ie, ≥18 years of age with a body mass index (BMI) \>40, or is \<18 years of age with a BMI in the 99th percentile plus 5 units at screening, in whom there is a causal relationship between obesity and the development of FSGS * History of alcohol or illicit drug use disorder * History of serious side effect or allergic response to any angiotensin II antagonist or endothelin receptor antagonist * Female patient is pregnant, plans to become pregnant during the course of the study, or is breastfeeding. Key Inclusion Criteria for the Open-label Extension Based on assessments at the Week 108 visit: * Complete participation in the double-blind period, including the Week 112 visit. * Patient received blinded study medication through the duration of the double-blind period (ie, did not permanently discontinue study medication) Key Exclusion Criteria for the Open-label Extension Based on Assessments at Week 108 and 112 visits: * Progression to end-stage renal disease requiring replacement therapy * The patient developed criteria for discontinuation between Week 108 and Week 112 * The patient was unable to initiate, or developed contraindications to, treatment with RAAS inhibitors between Week 108 and Week 112 * eGFR ≤20 mL/min/1.73 m2 at Week 108