A Rare Kidney Disease You've Never Heard Of—But Should Know About

Focal segmental glomerulosclerosis (FSGS) is a rare kidney disease that causes scarring in the tiny filters responsible for cleaning your blood, potentially leading to kidney failure if left untreated. While only about 7 out of every 1 million people are diagnosed with FSGS each year, the condition deserves attention because early detection and proper treatment can significantly slow disease progression and help protect remaining kidney function.

What Exactly Is FSGS and Who Gets It?

FSGS damages the glomeruli—the microscopic filters in your kidneys that remove waste and extra fluid from your blood. When some of these filters become scarred, your kidneys cannot work as efficiently. Over time, this scarring can lead to kidney failure, also called end-stage renal disease (ESRD) or end-stage kidney disease (ESKD).

The disease affects both children and adults, though men are slightly more likely to develop it. People who are Black or African American have higher rates of FSGS compared to other populations. Doctors classify FSGS into three main types based on what causes it: primary FSGS (no clear cause, immune-mediated), secondary FSGS (caused by another health condition or factor), and genetic FSGS (caused by inherited gene mutations).

Why You Might Not Notice FSGS Until It's Advanced

One of the most dangerous aspects of FSGS is that in its early stages, you may have no symptoms at all. This silent progression is why regular kidney health screenings matter. As the disease advances, symptoms can include:

• Swelling: Puffiness in your legs, ankles, feet, or around your eyes from fluid buildup
• Sudden Weight Gain: Rapid weight increase from fluid retention rather than fat gain
• Fatigue: Feeling more tired than usual due to waste buildup in your body
• Foamy or Bubbly Urine: A sign that protein is leaking from your kidneys into your urine
• Dark or Cola-Colored Urine: An indicator of blood in your urine
• High Blood Pressure: Which can further damage your kidneys if not controlled

Some people with FSGS develop nephrotic syndrome, a condition where the kidneys leak large amounts of protein. This can cause additional complications including high fat levels in the blood, increased risk of blood clots, and increased risk of infections.

How Doctors Diagnose FSGS

The only way to definitively confirm FSGS is through a kidney biopsy. During this procedure, your doctor uses a needle and imaging (such as ultrasound or CT scan) to take a tiny piece of kidney tissue to examine under a microscope. This is important because many kidney diseases look similar on standard lab tests, so a biopsy helps identify the exact type of FSGS to guide treatment decisions.

Before a biopsy, doctors typically order several tests to assess kidney function and look for signs of disease:

• Blood Tests: eGFR (estimated glomerular filtration rate) measures how well your kidneys are filtering waste
• Urine Tests: uACR (albumin-to-creatinine ratio) and uPCR (protein-to-creatinine ratio) measure how much protein is leaking into your urine
• Genetic Testing: Identifies inherited gene mutations like APOL1 that can cause FSGS
• Viral Testing: Rules out secondary causes such as HIV, COVID-19, or other infections

Treatment Options Depend on Your FSGS Type

FSGS is a chronic condition with permanent scarring that cannot be reversed. However, over half of people with FSGS can slow disease progression and protect their remaining kidney function with appropriate treatment and regular medical follow-ups. The current treatment approach focuses on protecting kidney filters, reducing protein in the urine, and tailoring therapy based on what caused your FSGS.

"The current focus and goal is protecting the kidney filters, reducing protein in the urine, and tailoring treatment based on the cause of your FSGS," according to information from the American Kidney Fund. Treatment typically includes a combination of medications and lifestyle changes.

Steps to Managing Your FSGS and Slowing Progression

• Blood Pressure Medications: Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) help protect your kidneys from further damage
• Diuretics: Water pills help reduce swelling by helping your kidneys eliminate excess salt and water
• Immunosuppressants: Medicines like glucocorticoids (steroids) or calcineurin inhibitors lower immune system activity and reduce inflammation
• Kidney-Friendly Diet: Follow a diet plan designed for kidney health, which typically means limiting sodium, controlling protein intake, and managing fluid consumption
• Regular Physical Activity: Aim for 30 minutes of activity most days of the week to support overall health
• Smoking Cessation: Quit smoking and avoid other tobacco products, which can accelerate kidney damage
• Treat Underlying Conditions: If secondary FSGS is the cause, managing or stopping the triggering factor (such as discontinuing a harmful medication or treating an infection) is essential

For people with secondary FSGS caused by another health condition, treating that underlying cause can help slow ongoing kidney damage. For example, if obesity is contributing to FSGS, weight management becomes part of the treatment plan. If a specific medication is causing the problem, your doctor may recommend stopping or switching that drug.

What Happens If FSGS Progresses to Kidney Failure?

If FSGS advances to kidney failure, treatment options like dialysis or kidney transplant can help you survive. However, FSGS can sometimes return after a kidney transplant—a complication called recurrence that happens in about 50 percent of people with primary FSGS. If recurrence occurs, treatments such as plasmapheresis (a procedure that filters harmful substances from your blood) and certain medications may help control it.

The key takeaway is that while FSGS is serious and irreversible, early detection combined with personalized treatment can make a significant difference in your long-term kidney health. If you notice symptoms like persistent swelling, foamy urine, or sudden weight gain, contact your doctor right away. And if you have a family history of FSGS or kidney disease, discuss genetic testing and screening options with your healthcare provider.