What is focal segmental glomerulosclerosis (FSGS)?

Focal segmental glomerulosclerosis (FSGS) is a type of nephrotic syndrome - a rare kidney condition that causes too much protein to be lost in the urine and too much water to be retained in the body.

The term FSGS is used to describe a specific pattern of kidney damage that doctors see when they examine tissue from a kidney biopsy under a microscope.

FSGS is very rare. Nephrotic syndrome affects around 1 in 10,000 people a year in the UK. Around 1 in 4 of these will be diagnosed with FSGS.

Your kidneys contain about a million tiny filters called glomeruli. These can be damaged and scarred by nephrotic syndrome. FSGS describes a particular pattern of scarring.

• focal – some but not all of the glomeruli are affected
• segmental – a segment (part) of each glomerulus is scarred
• glomerulosclerosis – there is scarring on the glomeruli (‘sclerosis’ means scarring)

What causes FSGS?

There are two types of FSGS:

Primary or idiopathic FSGS occurs without a clear underlying cause. Doctors believe it may be related to factors in the blood that damage the kidney filters. This may be linked to a fault in the immune system, which is the body’s way of protecting itself from infection.

Secondary FSGS occurs because of other factors such as:

• Other medical conditions
• Medications
• Having reduced kidney tissue
• Long-term high blood pressure
• Infections

What are the signs and symptoms of FSGS?

If you have kidney damage which shows the FSGS pattern, you usually develop symptoms of nephrotic syndrome. These include:

• protein in the urine (proteinuria) – this is likely to only be seen under a microscope or when tested by dipping a specially treated paper strip into your urine (urine dipstick). However, if there is a lot of protein, the urine may look frothy.
• swelling or puffiness (oedema) – this can develop in different parts of the body, especially around the eyes and ankles. Swelling around the eyes tends to be worse first thing in the morning and improve as the day goes on whereas ankle swelling is usually worse in the evenings. The swelling is soft and puffy and leaves a dent if you press on it. There is no pain associated with the swelling. It is not an allergic reaction but is caused by the kidneys retaining too much water.
• increased risk of infection
• anaemia
• low blood pressure.

How is FSGS diagnosed?

Understanding the cause of the FSGS pattern in your kidneys is important because:

• It helps doctors choose the right treatment
• It allows them to better predict how the condition might progress
• It helps them understand if other family members might need testing
• It guides decisions about long-term care

Your kidney team will do various tests to try to understand the cause of your FSGS. They will explain which type of FSGS they think you have and why.

If your doctor thinks that you have FSGS, you may be referred to a hospital to see a nephrologist, a specialist kidney doctor.

Your doctor may suspect FSGS if you have symptoms of nephrotic syndrome and:

• have visible blood in your urine (haematuria)
• are urinating less often or smaller amounts
• have high blood pressure (hypertension)
• blood tests show that your kidneys are not working properly
• are a child or teenager
• have nephrotic syndrome that keeps coming back (frequently relapsing) in spite of treatment.

FSGS is diagnosed by a kidney biopsy. This is a procedure where a tiny piece (sample) of one of your kidneys is removed from the body by a special needle. This sample is examined under microscopes to find out more about the kidney’s health.

Blood tests will be done to check protein levels in your blood, and your kidney function. Blood may also be taken for genetic testing.

Does FSGS affect other parts of the body?

During flare-ups of nephrotic syndrome (when swelling occurs), people are more at risk of infections or of developing blood clots, particularly in the veins of the legs (thrombosis).

Does FSGS run in families?

Some cases of FSGS are due to a genetic mutation that affects the structure of part of the glomerulus in the kidney, which causes the protein leak. Your doctor will talk to you about this and may arrange for a genetic test to be done to see if other family members are affected, but this is very rare.

How is FSGS treated?

The FSGS pattern of scarring that is seen on a kidney biopsy is permanent. However, the underlying process that causes the scarring can be treated.

Successful treatment means achieving remission - when the protein leakage stops (complete remission) or significantly reduces (partial remission). Some people may continue to have protein leakage despite treatment.

Steroids

The first treatment for nephrotic syndrome is steroid medication, usually prednisolone. Steroids are chemicals that suppress the immune system or make it less active. Your doctor will give you more information about how and when you should take the medicine.

It is important that you take the steroids exactly as your doctor has told you, even if you are getting better. Stopping steroids suddenly can make you very unwell, so you should only stop taking steroid medicines on the advice of your doctor.

Immunosuppressants

If your nephrotic syndrome is caused by FSGS, you may also need stronger medicines called immunosuppressants. There are different types of immunosuppressants, and you may need to try more than one, sometimes in combination, to treat your FSGS. They include:

• tacrolimus
• mycophenolate mofetil – also called MMF

Other medication

Some people will be prescribed further medications such as:

• Antibiotics (usually penicillin) to prevent or treat infection
• Diuretics (water tablets) to reduce the water retention that causes swelling
• Angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) to reduce the amount of protein lost in the urine

Your kidney team will monitor how well your treatment is working by:

• regular urine tests to measure protein levels
• blood tests to check kidney function
• blood pressure measurements
• monitoring for any new symptoms or side effects

Contact your doctor if you have any of the following symptoms while on steroid medicines:

• fever (temperature above 38°C), with a sore throat or a cough
• a rash or severe bruising
• bad stomach pain or repeated vomiting – sometimes steroids can cause ulcers in the stomach.

Dietary changes

You may need to make temporary changes to what you eat. For example, you may need to eat less salt while you have swelling or puffiness or are taking steroids. This is because higher levels of salt in the body cause the kidneys to retain more water.

Your healthcare team will give you more information on this if it applies to you.

Some people with FSGS recover or go into remission. However, for most people the condition will get worse over time and will eventually lead to kidney failure and the need for dialysis and/or a transplant.

Where can I get more information or support about FSGS?

For more information on FSGS, including its genetics, diagnosis, symptoms and treatment, visit Nephrotic Syndrome Trust.

Publication date: 08/2025

Review date: 08/2028