Study of Sparsentan Treatment in Pediatrics With Proteinuric Glomerular Diseases

This is a multicenter, open-label, 112-week study of sparsentan in approximately 67 pediatric subjects aged ≥1 year to \<18 years with selected proteinuric glomerular diseases, divided into 3 populations, defined as follows: * Population 1: Subjects with selected proteinuric glomerular diseases associated with Focal Segmental Glomerulosclerosis (FSGS) and Minimal Change Disease (MCD) histological patterns * Population 2: Subjects with kidney biopsy-confirmed immunoglobulin A nephropathy (IgAN), immunoglobulin A vasculitis (IgAV), or Alport syndrome (AS) * Population 3: Subjects with kidney biopsy-confirmed IgAN The study will evaluate long-term safety, tolerability, and efficacy with pharmacokinetic (PK) evaluations at Day 1 (Baseline), Day 2 (Visit 4), and Week 12 (Visit 9) in Population 1 and Population 2. In Population 3, PK values will be evaluated at Day 1 (Baseline) and at Weeks 4, 8, 12, 24, 36, 48, 60, 72, 84, and 96. For Population 1 and Population 2, subjects will be enrolled in 3 cohorts based on age ranges. For Population 3, subjects will be enrolled in one cohort. Study Enrollment: * Population 1: FSGS and/or MCD (30 subjects total) 1. Cohort 1 (6 subjects): ≥8 years to \<18 years 2. Cohort 2 (18 subjects): ≥3 years to \<8 years 3. Cohort 3 (6 subjects): ≥1 year to \<3 years * Population 2: IgAN, IgAV, or AS (27 subjects total) 1. Cohort 1 (9 subjects): ≥8 years to \<18 years 2. Cohort 2 (12 subjects): ≥5 years to \<8 years 3. Cohort 3 (6 subjects): ≥2 years to \<5 years * Population 3: IgAN (10 subjects total) 1. 10 subjects: ≥8 years to \<18 years