Due to disease-specific changes of glomerular permeability [47], different patterns of plasma proteins including transferrin, α1 antitrypsin (A1AT), and antithrombin III would be lost in urine of patients with nephrotic syndrome and might not be specific for FSGS as they could be detected in nephrotic range proteinuria secondary to any etiology [54]. This evidence concerns the gene SERPINA1 and focal segmental glomerulosclerosis.