3. Children greater than 20 kilograms, will be eligible for all branches of the study except for treatment of steroid resistant FSGS with pirfenidone, as pirfenidone has not previously been administered to pediatric patients in any setting. Children less than 20 kilograms will be excluded from the study for the following reason: plasma exchange in patients less than 20 kilograms requires a red blood cell transfusion, which significantly increases the risk of the procedure by exposing the patient to the risk of transfusion associated infections, and the safety of an aggressive course of plasma exchange has not been established in this population.