Nephrotic syndrome results from increased permeability of the glomerular basement membrane, causing massive proteinuria, hypoproteinemia, hyperlipidemia, and edema. The main types are minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and membranoproliferative glomerulonephritis. Treatment involves corticosteroids, with alternatives like cyclophosphamide for frequent relapsers or resistant cases. Complications include infections, thrombosis, and progressive kidney damage if long-term corticosteroid use is required.