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What is idiopathic nephrotic syndrome?

Idiopathic nephrotic syndrome (INS) occurs when the structure of the filter within the kidney breaks down. When this happens due to genetic mutations it is known as nephrotic syndrome (NS), however if a genetic mutation cannot be found then it is termed idiopathic. The cause is not well understood but there is good evidence that it is caused by an unknown factor in the circulation released by the immune system 

Causes of idiopathic nephrotic syndrome

INS is a type of nephrotic syndrome that has no known genetic cause. The specific underlying triggers for INS are not well understood, although there is growing evidence that there is something in the bloodstream that travels to the kidney and damages cells known as podocytes. The podocytes are octopus-like cells that sit on top of the small blood vessels and wrap their tentacles around them. When the podocytes are damaged by this unknown factor, protein can leak into the urine causing nephrotic syndrome

Idiopathic nephrotic syndrome symptoms

Though they have different causes, the symptoms of INS and NS are the same since the problem in the structure of the filtration barrier is very similar. These symptoms can include: 

  • Frothy urine: the urine can appear foamy because it contains protein 
  • Oedema: this term describes swelling that is commonly found in the feet, ankles and around the eyes 
  • Weight gain: due to the body retaining more water 
  • Fatigue 
  • Loss of appetite 
  • Infections due to the loss of antibodies (which are proteins) into the urine 

Idiopathic nephrotic syndrome diagnosis

Following a thorough physical examination and review of personal medical history or relevant conditions in family members, the urine will be tested for the presence of protein. A blood test may also be performed to check kidney function. The levels of important markers including albumin, creatinine, sodium, and potassium can indicate how well the kidneys are filtering the blood. A kidney biopsy may also be needed to assess the structure of the filtering parts of the kidney.  

You may come across terms such as focal segmental glomerulosclerosis (FSGS) or minimal change disease (MCD). These terms describe how the kidney tissue looks under the microscope. Both FSGS and MCD are forms of nephrotic syndrome or idiopathic nephrotic syndrome. These tests may establish a diagnosis of nephrotic syndrome if genetic causes are likely if the person is a small child or there is a family history. These people will undergo genetic testing. Otherwise, people will be put on a course of steroids or other immunosuppressants.

Idiopathic nephrotic syndrome treatment

Initially INS will be treated with steroids. Usually, a high dose of prednisolone is given initially which is then gradually reduced, this can stop symptoms for some time (known as ‘remission’). However, in around 20% of people, steroid treatment is ineffective.  

In these cases, often called 'steroid-resistant INS’, different medications including range drugs that suppress different parts of the immune system may be used, such as calcineurin inhibitors, alkylating agents, or rituximab, as well as ACE inhibitors to bring the symptoms under control. The immunosuppression by any of these treatments can lead to remission. 

If steroid treatment is effective prognosis is generally good. INS can come back once the person has come off steroids, however many people find that steroid treatment can control their INS. Prognosis is better in people who experience their first episode before the age of five and if their first episode is sensitive to steroids. MCD has a better prognosis than FSGS. If other therapies are successful in steroid resistant INS then prognosis is generally good. However, in people whose INS is not put into remission following intensive treatment with immunosuppressants, the condition can progress to chronic kidney disease and end-stage renal failure requiring dialysis and or transplant.  

Reviewed Jan 2024

A lady with blonde bobbed hair, black glasses and a black jumper with her arms folded, smiling to the camera.

"Our aim is to personalise nephrotic syndrome treatment, so that patients can avoid medications that don’t work for them."

Dr Samantha Hayward

Researcher spotlight

Dr Samantha Hayward from the University of Bristol has been awarded a grant to develop a tool which will help personalise treatment for children with nephrotic syndrome.

Samantha will investigate whether steroids change the chemical tag on patients’ DNA and will use this information to update the prediction tool. This will make sure that the tool can accurately predict responses to treatment regardless of how much steroid treatment a patient has already received. 

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