What Causes Nephrotic Syndrome? Nephrotic Syndrome can be “primary” or “secondary” in nature. Primary Nephrotic Syndrome Most often, Nephrotic Syndrome is defined by its primary diseases that attack the kidney’s filtering system. Doctors often call these diseases “idiopathic,” which means that they have arisen from an unknown cause. Minimal Change Disease (MCD) – most common in children Focal Segmental Glomerulosclerosis (FSGS) Membranous Nephropathy (MN) – most common in adults Secondary Nephrotic Syndrome Secondary NS is associated with an underlying cause or condition. You may have secondary nephrotic syndrome if you have also been diagnosed with one of the following: Vasculitis: Lupus Infection: Hepatitis, HIV, CMV, others Metabolic disorder: Diabetes Cancer: Lymphoma Amyloidosis Renal Vein Thrombosis Heart Failure: Constrictive Pericarditis Medications, toxins, IV drug abuse