This multicenter, prospective, single-arm clinical study will evaluate the probable benefit and safety of the LIPOSORBER® LA-15 System for the treatment of adult patients with nephrotic syndrome associated with primary focal segmental glomerulosclerosis, when the standard treatment options, including corticosteroid and/or calcineurin inhibitors treatments, have been unsuccessful or not well tolerated, and the patient has a GFR ≥ 45 ml/min/1.73m2, or the patient has post-renal transplant recurrence. Treatment for FSGS is considered unsuccessful if the patient is unresponsive to standard therapy (e.g., at least 8 weeks of corticosteroids) and fails to achieve complete or partial remission. A standard treatment is considered not well tolerated if the patient experiences severe side effects without providing an acceptable level of clinical benefit.