Nephrotic syndrome is a collection of symptoms that occur because tiny filters (glomeruli) in the kidney become leaky. The glomeruli (a single one is called a glomerulus) are tufts of capillaries (the smallest type of blood vessels). They act as filters in the kidneys, allowing a certain amount of water and waste products to leave the blood and eventually pass out of the body in the form of urine. Normally, proteins are unable to pass through the glomerular filter. However, in people with nephrotic syndrome, this filter becomes defective, allowing large quantities of protein to leave the blood circulation and pass out of the body in the urine.

Patients with nephrotic syndrome are from all age groups, but children between 18 months and four years are at increased risk for the disorder. In children, boys are more frequently affected; in adults, the ratio of men to women...