A Study of the Efficacy and Safety of DMX-200 in Patients With FSGS Who Are Receiving an ARB

DOUBLE BLIND PERIOD Inclusion Criteria: 1. Patients must be 12 to 80 years old 2. A diagnosis of primary FSGS, genetic FSGS, or FSGS of undetermined cause. Confirmed by kidney biopsy within 7 years of screening 3. Must be either receiving an ARB at the maximal tolerated dose or willing to transition 4. If taking corticosteroids, the dosage must be stable for ≥4 weeks prior to Screening and during Stabilization 5. If taking aldosterone inhibitors, mineralocorticoid receptor antagonists, direct renin inhibitors, sodium-glucose co-transporter-2 (SGLT2) inhibitors, or endothelin receptor antagonists (ERAs, including dual antagonists), the dose and regimen must be stable for ≥12 weeks prior to Screening and during Stabilization 6. Urine PCR \>1.5 g/g (\>169.5 mg/mmol) or 24-hour total protein \>1.5 g/day based on 24-hour urine collection during Screening. 7. Estimated eGFR ≥25 and ≤120 mL/min/1.73 m2 at Screening for adults \& eGFR ≥25mL/min/1.73 m2 for adolescent patients (\<18 years) 8. Seated blood pressure ≤160/100 mm Hg (mean of 3 values) (patients ≥18 years of age) or between the 5th and 95th percentile for age, sex, and height (patients \<18 years of age) at Screening 9. Body weight ≥35 kg (all patients) AND a body mass index (BMI) ≤40 kg/m2 (patients ≥18 years of age) or between the 5th and 98th percentile for age and sex (patients \<18 years of age) at Screening. 10. A female patient is eligible to participate if she is not pregnant or planning to become pregnant during the study, not breastfeeding, and at least one of the following conditions applies: 1. Is not of childbearing potential 2. If of childbearing potential and beginning at menarche, agrees to use a highly effective method of contraception consistently during the treatment period. 11. A male patient with a female partner of childbearing potential is eligible to participate if he agrees to use acceptable contraception 12. A patient or parent/legal guardian (as appropriate) who is capable of giving signed informed consent, and where required, the patient is capable of providing assent. Exclusion Criteria: 1. Has FSGS secondary to another condition. 2. Patients with nephrotic syndrome (\>3.5 g/day proteinuria and serum albumin \<30 g/L) who have not previously been treated with standard of care FSGS-directed therapies (including steroids). 3. History of type 1 diabetes mellitus, or uncontrolled type 2 diabetes mellitus (defined as glycated hemoglobin \[HbA1c\] \>8% at Screening) 4. History of lymphoma, leukemia, or any active malignancy within the past 2 years (except for basal cell or squamous cell carcinomas of the skin or cervical carcinoma in situ that have been resected and with no evidence of metastatic disease). 5. Active clinically significant hepatobiliary disease. 6. Documented history of heart failure (New York Heart Association Class III/IV) or a major adverse cardiac event within 12 weeks prior to Screening. 7. Has a physical, medical, or psychological condition, that in the opinion of the Investigator, may interfere with the evaluation the study. 8. The patient has a history of alcohol or illicit drug use disorder within 1 year prior to Screening. 9. Had a prior organ transplant or stem cell transplant, with the exception of corneal transplant. 10. Positive screening assessment for viral hepatitis B surface antigen, or anti-hepatitis C virus (HCV) antibody AND positive HCV RNA, or human immunodeficiency virus 1 and 2. 11. Serum potassium levels \>5.5 mmol/L at Screening. 12. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) \>2 × upper limit of normal (ULN) at Screening. 13. Treatment with non-steroid immunosuppressant agents including biological drugs (e.g. rituximab), calcineurin inhibitors, cyclophosphamide, azathioprine, or mycophenolate mofetil within 12 weeks prior to Screening. 14. History of serious side effects or allergic response to an angiotensin II antagonist or has a known sensitivity to any components in the IP. 15. Unable to swallow oral medication. 16. Prior participation in any Dimerix-sponsored DMX-200 clinical study. 17. Participation in a clinical study with an investigational product (IP) within 28 days or 5 half-lives (whichever is longer) prior to Screening or plans to participate in another study during the course of this study. 18. Are study site personnel directly affiliated with this study and their immediate families OLE PERIOD Inclusion Criteria: 1. A patient or parent/legal guardian (as appropriate) who is capable of giving signed informed consent, and where required, the patient is capable of providing assent. 2. Patients who have completed participation in the double-blind period, including the Week 104 visit, and who may derive benefit from (continued) treatment with DMX-200, and/or continued follow-up 3. The patient received blinded Investigational Product throughout the duration of the double-blind period up to the Week 104 visit 4. The patient continues to meet the contraceptive requirements Exclusion Criteria: 1. The patient has met the criteria for permanent IP discontinuation or study discontinuation 2. Any safety concerns identified during the double-blind period which, in the Investigator's opinion, may interfere with the patient's continued participation during the OLE period.