All about nephrosis

Nephrosis is a catch-all word which can mean different things to different people. Many physicians prefer to use the term nephrotic syndrome. This refers to a kidney disorder manifested by the following:

  • A massive leak of protein (albumin) into the urine (proteinuria)
  • A low blood level of albumin due to the large amounts lost in the urine
  • An increased level of cholesterol in the blood
  • Retention of fluid in the body (edema) causing swelling

Nephrotic syndrome, which affects both kidneys, refers to all four of the above findings occurring together. Several different kidney diseases can cause the syndrome. A renal biopsy is sometimes necessary to help distinguish among the possibilities. In children, the most common kidney disease causing the condition is called minimal-change nephrotic syndrome (sometimes also referred to as minimal-lesion nephrotic syndrome). This condition accounts for about 80% of all cases of nephrotic syndrome occurring in children less than ten years of age.

In almost all cases, there is no obvious cause and the condition is included under the general term, "idiopathic nephrotic syndrome.” (Idiopathic is a term meaning that the cause of the disease is not known.) It is called minimal-change nephrotic syndrome because examination of kidney tissue using a conventional microscope reveals an appearance that is practically normal. The typical signs of inflammation that are seen in other kinds of kidney disease are not seen.

There is another kidney disease in the general category of idiopathic nephrotic syndrome, focal segmental glomerulosclerosis or, for short, FSGS, a more severe type of nephritic syndrome that is steroid resistant. The remainder of this discussion will use the term nephrosis to mean minimal-change nephrotic syndrome.

What causes minimal-change nephrotic syndrome?

The cause is not known. However, there is no relationship to a "strep throat" or evidence of direct invasion of the kidney by germs, such as bacteria or viruses. Often, the disease begins when a child has a minor respiratory illness such as a cold but it is not understood how a virus triggers a leak of protein into the urine. There is also no proven relationship of this disease to allergies, pollens, foods or medications. It is not contagious; one person cannot catch it from another person. It is not brought on by emotional stress. Since the cause of nephrosis is not known, we do not know of a way to prevent this illness. There is no immunization, change in activity, diet, climate, or medication that has been shown to have an effect on the prevention of this illness.

The difference between nephritis and nephrosis

Nephritis is a nonspecific term that covers several different kinds of kidney diseases which have, in common, an inflammation of the kidney filtering membrane causing not only a leak of protein into the urine (as in nephrosis), but also the presence of red blood cells in the urine (hematuria), high blood pressure (hypertension) and, sometimes, a decrease in the ability of the kidneys to clear waste products from the blood (kidney failure). The most common form of nephritis in children is one which develops 1 to 2 weeks following a "strep" infection of the throat or of the skin. On the other hand, minimal-change nephrotic syndrome is not associated with inflammation of the kidneys or a recent "strep" infection. It is also generally not associated with hypertension, red blood cells in the urine, or decreased clearing ability of the kidneys to remove waste products of metabolism from the blood. The major manifestations of minimal-change nephrotic syndrome are the four components of the nephrotic syndrome mentioned above. The following discussion refers specifically to minimal-change nephrotic syndrome.

The kidney with nephrosis as compared to a healthy kidney

The main function of the kidneys is to filter the blood, removing or clearing waste products of metabolism, which are then excreted in the urine. The filtering membrane of a healthy kidney does not leak more than a minimal amount of blood protein (mainly albumin) into the urine, and the test of urine for the presence of albumin, using a dipstick test indicator is said to be “negative.”

In nephrosis, the filtering membrane of the kidney is altered so that it allows protein (albumin) to leak into the urine, giving a “positive” test for the presence of protein when the test strip is dipped in the urine specimen. The leak of large amounts of albumin into the urine causes depletion of blood albumin to low levels, which can be confirmed by a blood test. The low blood albumin level, in part, causes the kidneys to retain salt and water, and this retention of fluid (edema) causes swelling of various parts of the body. Such swelling may cause a distressing and drastic change in the appearance of the child. Although swelling due to fluid retention is painless, it is often emotionally upsetting to the young child.

Incidence of the condition

Nephrosis is a relatively uncommon disorder. It may be estimated that in an area with a population of about 7 million, there are about 50 to 60 children and adolescents with this disorder at any one time, and that over the course of a year, 20 to 25 new patients will be diagnosed (or about 2 out of every 100,000 children age 16 or less will develop this condition each year). Although minimal change nephrotic syndrome can begin at any age, children between the ages of 2 and 6 years are most often affected. It is less common in older children and rare in adults. Boys are more frequently affected than girls.

The condition does not usually run in families. In most instances, the affected child is the only one in the family with this condition. A child does not inherit nephrosis from a parent who may have had it as a child, except in very unusual circumstances. However, there are rare genetic forms of the nephrotic syndrome in which the susceptibility for the disease is passed from one or both parents to the child.

Research

There is active research going on in several pediatric kidney disease centers, including ours, and we are hopeful that the precise cause of nephrosis will eventually be discovered. This research has enabled us to learn much about the course of the disease, and it is now possible to make more accurate predictions as to the eventual outcome. The costs of such research are enormous and depend on funding by the National Institutes of Health (which means your tax dollars are contributing to such research) or funds from voluntary health agencies such as your local Kidney Foundation. The funding of research and education by the Kidney Foundation is made possible largely from small contributions by individual donors.

(Note: This set of pages has been adapted from an early version of “Questions Parents Ask About Nephrosis,” which was written by Dr. Ron Kallen and distributed for many years by the National Kidney Foundation. This 2006 version includes contributions by Drs. Craig B. Langman, Richard A. Cohn, Jerome C. Lane and H. William Schnaper. Janis Arnold, MSW, also made significant contributions.)