Nephrosis, or nephrotic syndrome, is a group of symptoms that affect both kidneys. Several different kidney diseases can cause the syndrome, and a kidney biopsy is sometimes necessary to help distinguish among the possibilities. In children, the most common kidney disease causing the condition is 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 younger than 10-years-old.
In almost all cases, there is no obvious cause, leading to a diagnosis of "idiopathic nephrotic syndrome.” (Idiopathic simply means that the cause of the condition is not known.) It is called minimal-change nephrotic syndrome because examination of kidney tissue using a conventional microscope reveals a generally normal appearance. The typical signs of inflammation seen in other kinds of kidney disease do not appear.
Another kidney disease in the general category of idiopathic nephrotic syndrome is focal segmental glomerulosclerosis (FSGS), a severe type of nephrotic syndrome that is usually steroid resistant. The remainder of this discussion will use the term nephrosis to mean minimal-change nephrotic syndrome.
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 generally is not inherited. 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.
The cause is generally not known. There is no relationship to a strep throat or evidence of direct invasion of the kidney by germs, such as bacteria or viruses, as in nephritis. 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. Nor is it brought on by emotional stress. Since the cause of nephrosis is unknown, we do not know of a way to prevent it. 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 most prominent symptoms include:
- 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, especially in the hands, feet and around the eye
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. This is diagnosed by dipping a test strip into a urine sample to check for the presence of albumin; if the kidneys are healthy, the test is read as negative.
In nephrosis, the filtering membrane of the kidney is altered so that it allows protein (albumin) to leak into the urine, leaving a positive test result for the presence of protein. The leak of large amounts of albumin into the urine causes lowered blood albumin 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 a young child.
Active research is ongoing in several pediatric kidney disease centers, including Ann & Robert H. Lurie Children’s Hospital of Chicago, 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 National Kidney Foundation of Illinios. The funding of research and education by the Kidney Foundation is made possible largely from small contributions by individual donors.