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Focal segmental glomerulosclerosis

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Focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a histopathologic finding of scarring (sclerosis) of glomeruli and damage to renal podocytes. This process damages the filtration function of the kidney, resulting in protein presence in the urine due to protein loss. FSGS is a leading cause of excess protein loss—nephrotic syndrome—in children and adults in the US. Signs and symptoms include proteinuria and edema. Kidney failure is a common long-term complication of the disease. FSGS can be classified as primary, secondary, or genetic, depending on whether a particular toxic or pathologic stressor or genetic predisposition can be identified as the cause. Diagnosis is established by renal biopsy, and treatment consists of glucocorticoids and other immune-modulatory drugs. Response to therapy is variable, with a significant portion of patients progressing to end-stage kidney failure. An American epidemiological study 20 years ago demonstrated that FSGS is estimated to occur in 7 persons per million, with male African-Americans at higher risk.

The most common symptoms are a result of abnormal loss of protein from the glomerulus of the kidney, and include:

Common signs are also due to loss of blood proteins by the glomerulus of the kidney, including:

FSGS is primarily a disease of the renal glomerulus, the site of filtration of ions and solutes. Podocytes are specialized cells lining the Bowman's capsule that contribute to the filtration barrier, preventing molecules larger than 5 nm from being filtered. FSGS involves damage to the renal podocytes such that larger molecules, most notably proteins, are filtered and lost through the kidney. Thus, many of the signs and symptoms of FSGS are related to protein loss.

On histology, FSGS manifests as scarring (sclerosis) to segments of glomeruli; moreover, only a portion of glomeruli are affected. The focal and segmental nature of disease seen on histology help to distinguish FSGS from other types of glomerular sclerosis.

FSGS can be classified by the putative cause of damage to podocytes. Primary FSGS involves cases in which no cause is readily identifiable. It is presumed that a set of unidentified circulating factors in the blood contribute to podocyte damage in these cases.

Secondary FSGS is caused by an identifiable stress or toxin that injures podocytes. Many causes of secondary FSGS contribute to podocyte injury through hyperfiltration, which is a scenario of excess filtration by renal glomeruli. Hyperfiltration can be caused by obesity, diabetes or loss of the contralateral kidney, among other causes.

Secondary FSGS can also be caused by toxins, including anabolic steroids and heroin.

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