Study of Sparsentan Treatment in Pediatrics With Proteinuric Glomerular Diseases

Inclusion Criteria for All Subjects (All Three Populations): A subject must meet all of the following criteria to be eligible for participation in this study: * The subject or parent/legal guardian (as appropriate) is willing and able to provide signed informed consent/assent, and where required, the subject is willing to provide assent before any screening procedures per local requirements. * The subject has an estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2 at screening. * The subject has a mean seated blood pressure between the 5th and 95th percentile for sex and height. Inclusion Criteria for Population 1: * The subject is male or female ≥1 year at screening and \<18 years of age at Day 1 (Baseline). * The subject has a UP/C ≥1.5 g/g (170 mg/mmol) at screening AND one of the following: * Kidney biopsy-proven FSGS or MCD histological patterns and clinical presentation consistent with primary FSGS or MCD and qualifying proteinuria at screening despite history or ongoing treatment with corticosteroids and/or other immunosuppressive disease-modifying agents. * Documentation of a genetic mutation in a podocyte protein associated with FSGS or MCD. Subjects with a documented podocytic mutation do not require kidney biopsy. * Kidney biopsy-proven FSGS histological pattern with medical history and clinical presentation consistent with maladaptive cause of the lesion. Note: The kidney biopsy may have been performed at any time in the past but must include light …