Focal segmental glomerulosclerosis, commonly called FSGS, is a pattern of scarring in the kidney’s filtering units that allows protein to leak into the urine and, if untreated, can progress to kidney failure. It is not a single disease but a collection of conditions that share one end result: parts of some glomeruli (the tiny clusters of blood vessels that filter waste) become hardened with scar tissue. The scarring is “focal” because it affects only some glomeruli and “segmental” because it damages only a portion of each affected one. Understanding which type of FSGS you have, what triggered it, and how aggressively to treat it can make a substantial difference in long-term kidney survival.
What Actually Happens Inside the Kidney
Each kidney contains roughly a million glomeruli. Wrapped around the blood vessels inside each glomerulus are specialized cells called podocytes, which extend tiny finger-like projections known as foot processes. These foot processes interlock to form a barrier that lets water and small waste molecules pass through while keeping large proteins, especially albumin, in the bloodstream. In FSGS, the podocytes are injured. Their foot processes flatten and pull apart in a process called effacement, and the barrier breaks down. Protein spills into the urine, and over time the affected glomerular segments scar shut.
Podocyte damage in FSGS is more severe than in some related conditions. Compared to minimal change disease, which can look similar early on, FSGS involves more pronounced structural changes in the foot processes, including detachment from the underlying membrane and abnormal buildup of internal structural proteins.1PubMed. Ultrastructural features and expression of cytoskeleton proteins of podocyte from patients with minimal change disease and focal segmental glomerulosclerosis This matters because podocytes barely regenerate in adults. Once enough of them are lost or damaged beyond repair, the scarring becomes irreversible.
Primary, Secondary, and Genetic Forms
One of the most important things doctors try to figure out after a biopsy shows FSGS is which category it falls into, because the cause determines the treatment.
- Primary FSGS: The immune system appears to produce a circulating factor that directly attacks podocytes. This form typically hits hard, causing heavy protein loss in the urine and full-blown nephrotic syndrome with swelling, low blood albumin, and high cholesterol. It responds (at least sometimes) to immunosuppressive drugs.
- Secondary FSGS: The scarring is a downstream consequence of something else overworking or injuring the kidneys. Common culprits include obesity, which increases blood flow and pressure inside glomeruli; reduced kidney mass from a prior injury or donation; viral infections like HIV; and certain drugs.2Nephron. Focal Segmental Glomerulosclerosis: State-of-the-Art and Clinical Perspective Uncontrolled diabetes and severe obesity can combine to accelerate the damage dramatically.3PubMed Central. Focal Segmental Glomerulosclerosis With Superimposed Infection‐Related Glomerulonephritis in a Diabetic Patient: A Case of Rapid Renal Decline Immunosuppression usually does not help here; the treatment targets the underlying cause.
- Genetic FSGS: Mutations in genes encoding podocyte proteins cause the cells to malfunction from birth or early life. This form also does not respond well to immunosuppressive therapy and tends not to recur after transplant, because the new kidney has normal podocyte genes.
Primary FSGS usually presents with sudden, heavy proteinuria and nephrotic syndrome, while secondary FSGS more often shows a slow increase in protein leakage over months or years, and patients may not develop full nephrotic syndrome even when proteinuria reaches high levels.4Clinical Kidney Journal. Differentiating primary and secondary FSGS using non-invasive urine biomarkers One microscopic clue that helps distinguish these forms is the degree of foot process effacement on electron microscopy. In primary FSGS, effacement is typically diffuse, ranging from about 88 to 100 percent of the foot process surface. In genetic FSGS, it tends to be far less extensive, from 0 to 38 percent.5PubMed Central. Degree of foot process effacement in patients with genetic focal segmental glomerulosclerosis: a single-center analysis and review of the literature
The Columbia Classification and Why Variants Matter
Under the microscope, not all FSGS scarring looks the same. The Columbia classification, published in 2004 and widely used since, divides FSGS into five histologic variants based on where and how the scarring occurs: collapsing, tip, cellular, perihilar, and not otherwise specified (NOS).6PubMed Central. Practical Application of Columbia Classification for Focal Segmental Glomerulosclerosis These are not just academic labels; they carry real prognostic weight.
The tip variant tends to have the mildest course. It is more common in white patients, carries the lowest injury scores, and has the slowest rate of progression. At three years in one clinical trial analysis, only about 7 percent of tip-variant patients had reached end-stage kidney disease. The collapsing variant sits at the opposite extreme. It is more common in Black patients, carries the highest injury scores and the highest baseline creatinine, and progresses fastest. Roughly 47 percent of collapsing-variant patients reached kidney failure within three years. The NOS variant fell in between, with about a 20 percent rate.7PubMed Central. Association of histologic variants in FSGS clinical trial with presenting features and outcomes These numbers illustrate why a biopsy report that simply says “FSGS” without specifying the variant is incomplete. The variant should inform how urgently treatment is escalated and how candidly the prognosis is discussed.
The Genetic Landscape
Dozens of genes have now been linked to FSGS. Most encode proteins that are critical to the podocyte’s structure or signaling. In children, recessive mutations in genes like NPHS1, NPHS2, LAMB2, and PLCE1 tend to cause severe, early-onset disease that progresses to kidney failure during infancy or childhood. Mutations in CD2AP and MYO1E cause childhood-onset disease with slower progression. In adults, dominant mutations in ACTN4, TRPC6, and INF2 are more common, typically producing proteinuria that first appears in the twenties or thirties and progresses to kidney failure over the following decade or two.8Korean Journal of Pediatrics. Genetics of hereditary nephrotic syndrome: a clinical review
One of the most significant genetic discoveries in nephrology in the past two decades involves APOL1, a gene found only in people with recent African ancestry. Certain APOL1 variants dramatically increase the risk of FSGS and other forms of kidney disease. In one landmark study, the odds ratio for idiopathic FSGS among African Americans carrying high-risk APOL1 genotypes was about 10.5, and for hypertension-attributed kidney failure it was 7.3.9PubMed Central. The apolipoprotein L1 (APOL1) gene and nondiabetic nephropathy in African Americans These variants likely became common because they protect against African sleeping sickness caused by trypanosomes, an evolutionary trade-off in which resistance to a parasitic infection came at the cost of kidney vulnerability.10PubMed Central. Apolipoprotein L1 and Kidney Disease in African Americans This discovery helps explain the long-observed disparity in FSGS rates between racial groups and has opened the door to targeted therapies — APOL1 inhibitors are now in clinical trials.
Who Gets FSGS and How Common Is It
FSGS is considered a rare disease, but “rare” in nephrology still adds up. A recent study of a racially and ethnically diverse patient population found that the average incidence of primary FSGS was about 1.7 per 100,000 patient-years. Rates were highest among Black patients (3.2 per 100,000), Pacific Islander patients (2.8), and Asian patients (2.7).11PubMed Central. Incidence and Proportion of Primary Focal Segmental Glomerulosclerosis (FSGS) among a Racially and Ethnically Diverse Adult Patient Population between 2010 and 2021 FSGS is the most common primary glomerular disease leading to kidney failure in the United States. In children with steroid-resistant nephrotic syndrome, which FSGS frequently underlies, the risk of reaching end-stage kidney disease within five years is around 50 percent if remission is not achieved.12Kidney International Supplements. Chapter 4: Steroid-resistant nephrotic syndrome in children
The Circulating Factor Mystery
A central puzzle of primary FSGS is the identity of the circulating factor that damages podocytes. Strong evidence for its existence comes from transplantation: FSGS can recur in a newly transplanted kidney within hours, far too quickly for a structural disease to develop from scratch. Something in the recipient’s blood injures the new kidney’s podocytes almost immediately.
Soluble urokinase plasminogen activator receptor, or suPAR, has been the most prominent candidate. It was elevated in the majority of patients in two geographically and ethnically distinct FSGS cohorts — about 84 percent in a North American trial group and 55 percent in a European cohort, compared with only 6 percent of controls.13PubMed Central. Circulating suPAR in two cohorts of primary FSGS In animal models, suPAR causes FSGS-like damage by binding to and activating a receptor on podocytes.14PubMed Central. Circulating permeability factor suPAR: from concept to discovery to clinic Changes in suPAR levels also track with remission during treatment, adding to the case that it plays a role in the disease process rather than being a bystander.15PubMed Central. Circulating suPAR in two cohorts of primary FSGS Still, suPAR can be elevated in other inflammatory conditions too, so the hunt for a definitive single biomarker continues.
Treatment of Primary FSGS
There are currently no FDA-approved drugs specifically for FSGS. Treatment has long been borrowed from other nephrotic conditions and relies heavily on immunosuppression, supportive care, and managing the downstream metabolic fallout of heavy proteinuria.
First-line therapy for primary FSGS has traditionally been high-dose corticosteroids (prednisone) given for months. These carry serious side effects including weight gain, bone loss, mood disturbance, and elevated blood sugar. More recently, calcineurin inhibitors like cyclosporine and tacrolimus have emerged as an alternative, either alongside or in place of high-dose steroids. A meta-analysis of trials in steroid-resistant patients found that cyclosporine increased the likelihood of proteinuria remission roughly sevenfold compared with placebo or supportive care alone.16PubMed Central. Calcineurin Inhibitors in the Treatment of Primary Focal Segmental Glomerulosclerosis: A Systematic Review and Meta-analysis of the Literature An initial approach combining a calcineurin inhibitor with lower-dose steroids has shown remission rates comparable to the traditional high-dose steroid regimen while reducing steroid exposure.17Kidney International Reports. Calcineurin Inhibitors With Reduced-Dose Steroids as First-Line Therapy for Focal Segmental Glomerulosclerosis
Rituximab, an antibody that depletes a type of immune cell called B cells, has gained traction for patients who relapse frequently or depend on high doses of other immunosuppressants. In a small study of adults with primary FSGS, 13 out of 14 patients achieved remission after rituximab, with a median time to remission of about 20 days, and steroids were discontinued in nearly all patients within six months.18Scientific Reports. Rituximab treatment of adults with primary focal segmental glomerulosclerosis These numbers come from a small, uncontrolled study, so they should be read with caution. Larger trials are needed, but the results are encouraging for people stuck in a cycle of relapse.
Regardless of immune therapy, nearly all FSGS patients benefit from drugs that reduce intraglomerular pressure, particularly ACE inhibitors and angiotensin receptor blockers. These medications lower proteinuria and slow progression independently of the underlying cause. Newer agents that block the renin-angiotensin-aldosterone system and SGLT2 inhibitors (originally developed for diabetes) are increasingly used as part of the supportive toolkit.
What Predicts a Good or Bad Outcome
Achieving remission of proteinuria — whether complete or partial — is the single strongest predictor of long-term kidney survival in FSGS. Several features at diagnosis help predict who will do well and who faces a steeper trajectory. Nephrotic-range proteinuria, reduced kidney function, low serum albumin, interstitial fibrosis and tubular atrophy on biopsy, and the absence of remission were all independently associated with worse long-term kidney outcomes in a large cohort analysis.19PubMed Central. Focal Segmental Glomerulosclerosis, Risk Factors for End Stage Kidney Disease, and Response to Immunosuppression The percentage of glomeruli with segmental scarring also matters: when more than about 20 percent of sampled glomeruli show sclerosis, the risk of adverse outcomes increases sharply.20Scientific Reports. A new index for the outcome of focal segmental glomerulosclerosis
The practical takeaway is that early and aggressive treatment aimed at reducing proteinuria gives the best chance of preserving kidney function. Waiting to see if proteinuria resolves on its own is generally not the strategy for primary FSGS.
Kidney Transplant and the Risk of Recurrence
For patients with primary FSGS whose kidneys fail, transplantation is the preferred treatment. But FSGS can come back in the new kidney, sometimes within hours of the operation. Recurrence rates vary across studies, but clinically significant recurrence affects a meaningful minority of transplant recipients.
Certain factors increase the risk. In pediatric patients, recurrence has been reported in as many as half of transplanted children in some series, compared with about 11 percent of adolescents and adults.21PubMed. Recurrence of focal segmental glomerulosclerosis in transplanted kidneys: analysis of incidence and risk factors in 59 allografts In adults, a large registry study found that older age at the time of original FSGS onset, white race, lower body mass index at transplant, and having had native kidney nephrectomies all predicted higher recurrence risk.22PubMed Central. Recurrence of FSGS after Kidney Transplantation in Adults Genetic FSGS, by contrast, rarely recurs in the transplant because the problem lay in the recipient’s own podocyte genes, not in a circulating factor.
Early foot process effacement on biopsy of the transplanted kidney, taken shortly after the organ is connected to blood flow, can predict whether recurrence is coming. In one study, the degree of effacement in these immediate post-transplant biopsies predicted nephrotic-range proteinuria with about 71 percent sensitivity and 92 percent specificity.23PubMed Central. Podocyte Foot Process Effacement in Post-reperfusion Allograft Biopsies Correlates with Early Recurrence of Proteinuria in Focal Segmental Glomerulosclerosis
When recurrence occurs, plasma exchange (to physically remove the presumed circulating factor) combined with rituximab has become a common strategy. A meta-analysis found that this combination achieved overall remission in about 73 percent of patients with post-transplant FSGS recurrence, with complete remission in roughly 41 percent and partial remission in about 32 percent.24PubMed. Combined rituximab and plasmapheresis or plasma exchange for focal segmental glomerulosclerosis in adult kidney transplant recipients: a meta-analysis Whether giving these treatments preemptively, before recurrence even starts, can prevent it entirely is the subject of an ongoing randomized trial.25Frontiers in Nephrology. A randomized controlled trial of preemptive rituximab to prevent recurrent focal segmental glomerulosclerosis post-kidney transplant (PRI-VENT FSGS): protocol and study design
Emerging Therapies
The treatment landscape for FSGS has been slow to evolve, but several genuinely new approaches are in clinical development. Sparsentan, a dual blocker of endothelin and angiotensin receptors, produced sustained reductions in proteinuria in the DUPLEX trial and is awaiting an FDA decision for a FSGS indication anticipated in 2026.26Nephrology Times. New Milestone in Targeted FSGS Therapy If approved, it would be the first drug specifically indicated for FSGS.
Beyond sparsentan, a range of mechanism-targeted agents are being studied. BI 764198, a selective inhibitor of the TRPC6 ion channel that is directly involved in podocyte injury, has reached phase 2 testing. APOL1 inhibitors are being developed specifically for the population carrying high-risk APOL1 variants. Other investigational approaches include TRPC5 channel modulators, SLIT2 antagonists, and additional endothelin receptor blockers like atrasentan.27Kidney Medicine. The Pursuit of New Treatments for Focal Segmental Glomerulosclerosis: Harmonizing Innovation With the DUET Study of Sparsentan The common thread is a move away from broad immunosuppression toward targeting specific molecular pathways in the podocyte.
Distinguishing FSGS Without a Biopsy
Kidney biopsy remains the gold standard for diagnosing FSGS, but it carries risks (bleeding, pain, and rarely loss of the kidney), and sampling error can miss the affected glomeruli entirely since the scarring is focal. Researchers are working on non-invasive alternatives. A urine biomarker panel of 93 proteins was recently shown to distinguish primary from secondary FSGS with an area under the curve of 0.95, achieving about 84 percent sensitivity and 100 percent specificity in the training cohort.28Clinical Kidney Journal. Differentiating primary and secondary FSGS using non-invasive urine biomarkers This kind of tool, once validated in larger populations, could help clinicians decide whether to pursue immunosuppression without requiring a biopsy — or at least prioritize who needs one most urgently.
Living With FSGS
The clinical literature tends to focus on lab numbers — proteinuria, creatinine, albumin — but these markers capture only part of the story. Qualitative research with FSGS patients has consistently found that fatigue is the most reported and most disruptive symptom, described as a profound exhaustion that interferes with routine tasks, work productivity, and social participation. Many patients consciously scale back their daily ambitions and build recovery time into their schedules. Despite its centrality to the disease experience, fatigue is often under-recognized by healthcare providers.29Glomerular Diseases. Lived Experiences of Patients and Care Providers in Focal Segmental Glomerular Sclerosis and IgA Nephropathy
Swelling, pain, anxiety, and the burden of managing medications with significant side effects — especially steroids — are other recurring themes. Patients describe a pervasive impact on physical, social, and mental quality of life regardless of whether they are adults or children.30PubMed Central. Health-Related Quality of Life in Focal Segmental Glomerular Sclerosis and Minimal Change Disease: A Qualitative Study of Children and Adults to Inform Patient-Reported Outcomes Standard lab-based measures of disease activity do not fully capture this burden, which has prompted calls for FSGS clinical trials to include disease-specific patient-reported outcome tools that are sensitive to the daily realities of living with the condition.31Clinical Kidney Journal. The longitudinal relationship between patient-reported outcomes and clinical characteristics among patients with focal segmental glomerulosclerosis in the Nephrotic Syndrome Study Network
For patients navigating a new FSGS diagnosis, the most actionable piece of information is that achieving even a partial reduction in proteinuria dramatically improves long-term outcomes. That means engaging early with a nephrologist who has experience managing glomerular diseases, being willing to try and adjust immunosuppressive regimens, and staying on supportive medications that protect the kidneys even when they do not feel like they are doing anything. Dietary sodium restriction, blood pressure control, and avoidance of nephrotoxic drugs round out the self-management picture. The disease is serious, but its trajectory is not set in stone at diagnosis.