Congenital nephrotic syndrome is a kidney condition that begins in infancy and typically leads to irreversible kidney failure (end-stage renal disease) by early childhood. Children with congenital nephrotic syndrome begin to have symptoms of the condition between birth and 3 months.

The features of congenital nephrotic syndrome are caused by failure of the kidneys to filter waste products from the blood and remove them in urine. Signs and symptoms of this condition are excessive protein in the urine (proteinuria), increased cholesterol in the blood (hypercholesterolemia), an abnormal buildup of fluid in the abdominal cavity (ascites), and swelling (edema). Affected individuals may also have blood in the urine (hematuria), which can lead to a reduced number of red blood cells (anemia) in the body, abnormal blood clotting, or reduced amounts of certain white blood cells. Low white blood cell counts can lead to a weakened immune system and frequent infections in people with congenital nephrotic syndrome.

Children with congenital nephrotic syndrome typically develop end-stage renal disease between ages 2 and 8, although with treatment, some may not have kidney failure until adolescence or early adulthood.

Mutations in the NPHS1 or NPHS2 gene cause most cases of congenital nephrotic syndrome. These genes provide instructions for making proteins that are found in the kidneys. Specifically, the proteins produced from the NPHS1 and NPHS2 genes are found in cells called podocytes, which are located in specialized kidney structures, called glomeruli, that filter the blood. The proteins are found at the podocyte cell surface in the area between two podocytes called the slit diaphragm. The slit diaphragm is known as a filtration barrier because it captures proteins from blood so that they remain in the body while allowing other molecules like sugars and salts to be excreted in urine. The proteins produced from the NPHS1 and NPHS2 genes also help relay cell signals.

Mutations in the NPHS1 or NPHS2 gene result in a decrease or absence of functional protein, which impairs the formation of normal slit diaphragms. Without a functional slit diaphragm, more molecules pass through the kidneys abnormally and get excreted in urine, including proteins and blood cells. The filtering ability of the kidneys worsens from birth, eventually leading to end-stage renal disease.

NPHS1 gene mutations cause all cases of congenital nephrotic syndrome of the Finnish type. This form of the condition is found in people of Finnish ancestry. NPHS1 gene mutations can cause congenital nephrotic syndrome in non-Finnish individuals, but they are a less common cause than NPHS2 gene mutations, which appear to be the most frequent cause of all cases.

Mutations in other genes cause a small number of cases of congenital nephrotic syndrome. Fifteen to 20 percent of individuals with congenital nephrotic syndrome do not have an identified mutation in one of the genes associated with this condition. In these cases, the cause of the condition may be environmental, including infections such as congenital syphilis or toxoplasmosis, or it may be caused by mutations in unidentified genes.

Normal Function

The NPHS1 gene provides instructions for making a protein called nephrin. Nephrin is primarily found in the kidneys, which are organs that filter waste products from the blood and remove them in urine. Specifically, nephrin is found in cells called podocytes, which are located in specialized kidney structures called glomeruli. Nephrin is located at the cell surface in the area between two podocytes called the slit diaphragm. The slit diaphragm is known as a filtration barrier because it captures proteins in blood so that they remain in the body while allowing other molecules like sugars and salts to be excreted in urine. Nephrin proteins on one cell interact with nephrin proteins on adjacent podocytes, forming a zipper-like structure. This structure allows the passage of small molecules through the slit diaphragm while preventing larger molecules like proteins from passing through. Nephrin proteins are essential for forming the slit diaphragm, anchoring the slit diaphragm to podocytes, and filtering blood.

Nephrin is also involved in cell signaling. It relays signals from outside the cell to inside the cell. Additionally, nephrin proteins on the surface of adjacent cells send and receive signals, allowing podocytes to communicate with one another.

Health Conditions Related to Genetic Changes

Congenital nephrotic syndrome

At least 250 mutations in the NPHS1 gene have been found to cause congenital nephrotic syndrome. This condition is a kidney disorder that begins in infancy and typically leads to irreversible kidney failure (end-stage renal disease) by early childhood.

NPHS1 gene mutations account for all cases of congenital nephrotic syndrome of the Finnish type. This form of the condition is found in people of Finnish ancestry. Two specific mutations, both of which result in an abnormally short, nonfunctional nephrin protein, account for nearly all cases. The first mutation, known as Finnmajor, is written as L41fsX90 and is responsible for 78 percent of cases. The second mutation, known as Finnminor, is written as R1109X and is responsible for 16 percent of cases.

NPHS1 gene mutations can also cause congenital nephrotic syndrome in non-Finnish individuals. Most of these mutations result in an abnormal nephrin protein that is trapped inside the cell and cannot get to the podocyte cell surface. A shortage of functional nephrin at the podocyte cell surface impairs the formation of normal slit diaphragms. Without a functional slit diaphragm, molecules pass through the kidneys abnormally and are excreted in urine. The filtering ability of the kidneys worsens from birth, eventually leading to end-stage renal disease.

Other Names for This Gene

• CNF
• nephrin
• nephrin precursor
• nephrosis 1, congenital, Finnish type (nephrin)
• NPHN
• NPHS1 nephrin
• renal glomerulus-specific cell adhesion receptor

Genomic Location

Normal Function

The NPHS2 gene provides instructions for making a protein called podocin. Podocin is primarily found in the kidneys, which are organs that filter waste products from the blood and remove them in urine. Specifically, podocin is found in cells called podocytes, which are located in specialized kidney structures called glomeruli. Podocin is located at the cell surface in the area between two podocytes called the slit diaphragm. The slit diaphragm is known as a filtration barrier because it captures proteins in blood so that they remain in the body while allowing other molecules like sugars and salts to be excreted in urine. Podocin likely helps bring other proteins that are needed for a functional slit diaphragm to the podocyte cell surface. The protein also is involved with podocyte cell signaling, helping the cell adapt to changes that occur during the filtration process.

Health Conditions Related to Genetic Changes

Congenital nephrotic syndrome

At least 170 mutations in the NPHS2 gene have been found to cause congenital nephrotic syndrome. This condition is a kidney disorder that begins in infancy and typically leads to irreversible kidney failure (end-stage renal disease) by early childhood. Mutations in this gene appear to be the most frequent cause of congenital nephrotic syndrome. Most NPHS2 gene mutations change single protein building blocks (amino acids) in the podocin protein. These mutations result in a reduction or absence of functional protein, which impairs the formation of normal slit diaphragms. Without a functional slit diaphragm, molecules pass through the kidneys abnormally and are excreted in urine. The filtering ability of the kidneys worsens from birth, eventually leading to end-stage renal disease.

Other disorders

NPHS2 gene mutations can cause other forms of nephrotic syndrome that develop later in life. In one form, called infantile nephrotic syndrome, signs and symptoms of the condition appear between 4 and 12 months of age. The features of this condition are similar to congenital nephrotic syndrome (described above), but they are often less severe. It is likely that NPHS2 gene mutations that cause infantile nephrotic syndrome have less effect on podocin function than those that cause congenital nephrotic syndrome, accounting for the later onset of the disorder.

Other Names for This Gene

• nephrosis 2, idiopathic, steroid-resistant (podocin)
• NPHS2 podocin
• PDCN
• podocin isoform 1
• podocin isoform 2
• SRN1

Genomic Location

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Nephrotic syndrome in children is most often treated with medicines.

Primary nephrotic syndrome

Corticosteroids. Corticosteroids, or steroids, are the medicines most often used to treat children with primary nephrotic syndrome. These medicines suppress the immune system, reduce the amount of protein passed into the urine, and decrease swelling.

In most children, treatment with corticosteroids will make nephrotic syndrome improve—also called “remission.” If symptoms return, called a “relapse,” the health care professional may prescribe a shorter course of corticosteroids until the disease goes into remission again. Although children may have multiple relapses, they often recover without long-term kidney damage. In most cases, relapses happen less often as children get older.

Although corticosteroids effectively treat nephrotic syndrome in many children, using these medicines for long periods of time can cause side effects, such as impaired growth, obesity, high blood pressure, eye problems, and bone loss. Other common side effects include anxiety, depression, and aggressive behavior. These problems are more likely to develop with larger doses and longer use.

In some cases, nephrotic syndrome may not improve with corticosteroids. Cases of nephrotic syndrome that don’t respond to corticosteroids are more difficult to treat than those that do. They are also more likely to progress to end-stage kidney disease.

Other medicines that suppress the immune system. If corticosteroids are not working or are causing harmful side effects, your child’s health care professional may prescribe other medicines that reduce the activity of the immune system. In some cases, your child may take these medicines together with low-dose corticosteroids.

Medicines for managing symptoms and complications. Health care professionals may also prescribe other medicines to help your child manage the symptoms and complications of nephrotic syndrome. Examples include

• angiotensin-converting enzyme (ACEs) inhibitors or angiotensin receptor blockers (ARBs) to lower blood pressure and help reduce protein loss
• diuretics, or water pills, to reduce swelling by helping the kidneys remove extra fluid from the blood
• statins to lower cholesterol
• blood thinners to treat blood clots

Children with nephrotic syndrome should get the pneumococcal vaccine and yearly flu shots to prevent viral and bacterial infections. They should also get age-appropriate vaccinations. But the health care professional may delay certain “live” vaccines—vaccines that use weakened forms of a virus—while your child is taking certain medicines.

Secondary nephrotic syndrome

Treatment focuses on the cause of nephrotic syndrome. For example, the health care professional may

• prescribe antibiotics to treat an infection that may be causing nephrotic syndrome
• change or stop any medicines your child takes that can cause nephrotic syndrome or make it worse, such as some medicines used to treat lupus, HIV, or diabetes

Your child’s health care professional may also prescribe the same medicines used to manage the symptoms and complications of primary nephrotic syndrome.

Congenital nephrotic syndrome

Treatment varies depending on whether the cause is genetic or an infection.

Genetic. Your child’s treatment will depend on the type of genetic mutation that is causing nephrotic syndrome and how bad the symptoms and complications are. Many children will lose kidney function over time and ultimately need a kidney transplant. To keep your child healthy until the transplant, the health care professional may recommend

• albumin injections to make up for the albumin passed in urine
• medicines to reduce swelling, lower blood pressure, and reduce protein loss
• removal of one or both kidneys to decrease the loss of albumin in the urine
• dialysis to filter wastes from the blood if the kidneys fail or if both kidneys are removed

Infection. When nephrotic syndrome is caused by a congenital infection, such as syphilis or toxoplasmosis, it will usually go away when the infection is treated.

Congenital nephrotic syndrome affects 1 to 3 per 100,000 children worldwide. In Finland, where this condition is particularly common, congenital nephrotic syndrome is estimated to affect 1 in 10,000 children.