This multi-center, open-label Phase 2 trial will study the safety, tolerability, and efficacy of bardoxolone methyl in qualified patients with the following rare chronic kidney diseases (CKD): CKD associated with type 1 diabetes (T1D), IgA nephropathy (IgAN), focal segmental glomerulosclerosis (FSGS), and autosomal dominant polycystic kidney disease (ADPKD). Patients will be enrolled in disease specific cohorts within the trial, and effectiveness of bardoxolone methyl in treating CKD will be assessed separately by cohort for each rare CKD.

All patients in the study will follow the same visit and assessment schedule. Following randomization on Day 1, patients will be scheduled to be assessed during treatment at Weeks 1, 2, 4, 6, 8, and 12, and by telephone contact on Days 3, 10, 21, 31, 38, and 45. Patients will also be scheduled to be assessed at an in-person follow-up visit at Week 16, four weeks after the end of treatment.

Inclusion Criteria:

• Male and female patients 18 ≤ age ≤ 65 upon study consent;
• Screening eGFR (average of Screen A and Screen B eGFR values) ≥ 30 and ≤ 90 mL/min/1.73 m2. The two eGFR values collected at Screen A and Screen B visits used to determine eligibility must have a percent difference ≤ 25%;
• Albumin to creatinine ratio (ACR) ≤ 2500 mg/g at Screen B visit;
• If receiving an angiotensin-converting enzyme (ACE) inhibitor and/or an angiotensin II receptor blocker (ARB), patients should be prescribed the maximally tolerated labeled daily dose (MTLDD) for at least 6 weeks prior to the Screen A visit;
• For patients enrolling in T1D Cohort: Diagnosis of type 1 diabetes confirmed by fasting C-peptide level. Diagnosis must have been made ≤ 35 years of age; and prescribed stable dose of insulin to maintain adequate glucose control for at least 6 months prior to the Screen A visit;
• For patients enrolling in IgAN Cohort: Biopsy-confirmed IgA nephropathy;
• For patients enrolling in FSGS Cohort: Biopsy-confirmed FSGS that is not due to known secondary causes including morbid obesity, decreased renal mass, viral infections, drug-induced nephrotoxicity, or prior history of vasculitis;
• For patients enrolling in ADPKD Cohort: Genetic confirmation of PKD1 mutation;
• Adequate bone marrow reserve and organ function at the Screen A visit as follows: Hematologic: Absolute neutrophil count > 1.5 x 109/L, platelets > 100 x 109/L, hemoglobin (Hgb) ≥ 9 g/dL; and Hepatic: Total bilirubin (TBL) ≤ 1.5 times the upper limit of normal (ULN), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 1.5 times ULN.

Exclusion Criteria:

• Kidney or any other solid organ transplant recipient or a planned transplant during the study;
• B-type natriuretic peptide (BNP) level > 200 pg/mL at Screen A visit;
• Acute dialysis or acute kidney injury within 12 weeks prior to Screen A visit or during Screening;
• Serum albumin < 3 g/dL at Screen A visit;
• Systemic immunosuppression for more than 2 weeks, cumulatively, within the 12 weeks prior to randomization or anticipated need for immunosuppression during the study;
• For patients enrolling in IgAN Cohort: Systemic manifestations of Henoch-Schonlein purpura within 1 year prior to Screen A visit; or have used belimumab, eculizumab, or rituximab within 6 months prior to Screen A visit;
• For patients enrolling in ADPKD Cohort: Receiving tolvaptan;
• Cerebrovascular event (stroke, transient ischemic attack) or aneurysm within 6 months prior to Screen A visit or during Screening;
• History of clinically significant left-sided heart disease and/or clinically significant cardiac disease;
• Uncontrolled systemic hypertension;
• Systolic BP < 90 mm Hg at Screen A visit after a period of rest;
• History of malignancy within 2 years prior to Screen A visit, with the exception of localized skin or cervical carcinomas;
• Uncontrolled diabetes (HbA1c > 10.0%) at Screen A visit;
• Untreated or uncontrolled active bacterial, fungal, or viral infection;
• Participation in other interventional clinical studies within 30 days prior to Day 1;
• Unwilling to practice acceptable methods of birth control (both males who have partners of child-bearing potential and females of childbearing potential) during Screening, while taking study drug, and for at least 30 days after the last dose of study drug is ingested;
• Women who are pregnant or breastfeeding.

In accordance with Biogen's Clinical Trial Transparency and Data Sharing Policy on https://www.biogentrialtransparency.com/