What is Nephrotic Syndrome?
Nephrotic Syndrome (NS) is not a disease but a collection of symptoms as a consequence of damaged kidneys. In particular, there tends to be generalized swelling of the body, especially around the eyes, feet, hands, and abdomen.Even though the majority of cases of NS are caused by diseases within the kidneys (primary), systemic (outside the kidney's) diseases can also cause kidney disease and NS.

Symptoms
Fever and symptoms of infection
Fatigue
Loss of appetite
Puffy eyelids
Weight gain
Scrotal swelling (fluid in the skin covering the testicles)
Bloated or distended abdomen (excess fluids)
Shortness of breath (Fluid in the Lungs)
Diarrhea
Low volume of urine
Anemia or Low Blood Pressure
Blood clots can block the blood flow to the kidneys

Cause
Primary kidney diseases -- fibrillary glomerulopathy, focal Glomerulonephritis, IgA nephropathy, Membranoproliferative Glomerulonephritis (i.e., MPGN, Minimal change disease and Rapidly progressive Glomerulonephritis).
Most primary causes have an association with immune system complexes (i.e., antibodies cause damage to the glomeruli.)
Systemic diseases -- Diabetes Mellitus, systemic lupus erythematosus, Multiple Myeloma, Amyloidosis, Chronic Lymphocytic Leukemias.
Hereditary diseases (e.g., passed on from parent to child), such as Alport's syndrome and Fabry's disease can also cause NS.