Nephrotic Syndrome

Introduction and Causes

Nephrotic syndrome is a common kidney disease characterized by heavy loss of protein in urine, low blood protein levels, high cholesterol levels and swelling. This disease can occur at any age but is seen more frequently in children compared to adults. Nephrotic syndrome is characterized by its cycle of response to treatment, manifested by gradual tapering and discontinuation of medication, treatment free period of remission and frequent relapses causing swelling. As the cycle of recovery and recurrence repeats for a long period (years), this disease is a matter of worry for both the child and the family.

What is nephrotic syndrome?

The kidney works as a sieve (filter) in our body that removes waste products and extra water from blood and passes them out via the urine. The size of the holes of these filters is so small so that in normal circumstances proteins that are large in size do not pass into the urine. In nephrotic syndrome the holes of these filters become large, so protein leaks into the urine. Because of the loss of protein in urine, the level of protein in the blood falls. Reduction of protein level in blood causes swelling (the medical term for the swelling seen in these patients is edema). The severity of edema varies depending on the amount of protein lost in the urine and reduction in protein level of blood. The kidney function (i.e., the ability to filter waste products or the glomerular filtration rate), per se, is normal in most patients with nephrotic syndrome.

What causes nephrotic syndrome?

In over 90% of children the cause of nephrotic syndrome (called primary or idiopathic nephrotic syndrome) is not known. Primary Nephrotic Syndrome is caused by four pathological types: minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy and membranoproliferative glomerulonephritis (MPGN). Primary nephrotic syndrome is a “diagnosis of exclusion”, i.e. they are diagnosed only after secondary causes have been excluded. In less than 10 % of cases, nephrotic syndrome may be secondary to different conditions such as infection, drug exposure, malignancy, hereditary disorders or systemic diseases such as diabetes, systemic lupus erythematosus and amyloidosis.

Minimal change disease

The most common cause of nephrotic syndrome in children is minimal change disease (MCD). This disease occurs in 90 percent of cases of idiopathic nephrotic syndrome in young children (under age six) and in 65% of cases in older children.

In a typical child with minimal change disease, blood pressure is normal, red blood cells are absent in urine and the values of serum creatinine and complement 3 (C3) are normal. Of all the causes of nephrotic syndrome, minimal change disease is the least stubborn, as over 90% of the patients respond well to steroid therapy.