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Focal segmental glomerulosclerosis
Classification and external resources
ICD-10 N00.-N08. (with .1 suffix)
ICD-9 581.1
OMIM 603278 603965 607832
MedlinePlus 000478
eMedicine med/2944
MeSH D005923

Focal segmental glomerulosclerosis (FSGS) is a cause of nephrotic syndrome in children and adolescents, as well as an important cause of kidney failure in adults.[1]

It is also known as "focal glomerular sclerosis" or "focal nodular glomerulosclerosis".[2]

It accounts for about a sixth of the cases of nephrotic syndrome.[3] (Minimal change disease (MCD) is by far the most common cause of nephrotic syndrome in children: MCD and primary FSGS may have a similar cause.[1])

Contents

Appearance

The individual components of the name refer to the appearance of the kidney tissue on biopsy: focal—only some of the glomeruli are involved (as opposed to diffuse), segmental—only part of an entire glomerulus is involved (as opposed to global), [4] glomerulosclerosis—refers to scarring of the glomerulus (a part of the nephron (the functional unit of the kidney)). The glomerulosclerosis is usually indicated by heavy PAS staining and findings of IgM and C3 in sclerotic segment.[5 ]

Classification

Depending on the cause it is broadly classified as

There are many other classification schemes also.

Pathologic variants

Five mutually exclusive variants of focal segmental glomerulosclerosis may be distinguished by the pathologic findings seen on renal biopsy:[6]

  1. Collapsing variant
  2. Glomerular tip lesion variant
  3. Cellular variant
  4. Perihilar variant
  5. Not otherwise specified (NOS) variant.

Recognition of these variants may have prognostic value in individuals with primary focal segmental glomerulosclerosis (i.e. where no underlying cause is identified). The collapsing variant is associated with higher rate of progression to end-stage renal disease, whereas glomerular tip lesion variant has low rate of progression to end-stage renal disease in most patients.[6] Cellular variant shows similar clinical presentation to collapsing and glomerular tip variant but has intermediate outcomes between these two variants. However, because collapsing and glomerular tip variant show overlapping pathologic features with cellular variant, this intermediate difference in clinical outcomes may reflect sampling bias in cases of cellular focal segmental glomerulosclerosis (i.e. unsampled collapsing variant or glomerular tip variant). The prognostic significance of perihilar and NOS variants has not yet been determined. The NOS variant is the most common subtype.[6]

Causes

There are currently several known genetic causes of the hereditary forms of FSGS.

Gene OMIM Description
FSGS1: ACTN4 603278 The first gene involved with this disorder is ACTN4, which encodes alpha-actinin 4. This protein crosslinks bundles of actin filaments and is present in the podocyte. Mutations in this protein associated with FSGS result in increased affinity for actin binding, formation of intracellular aggregates, and decreased protein half-life. While it is unclear how these effects might lead to FSGS there are a number of theories. Firstly, protein aggregation may have a toxic effect on the podocyte. Secondly, decreased protein half-life or increased affinity for actin binding may alter actin polymerization and thereby affect the podocytes cytoskeletal architecture.[7]
FSGS2: TRPC6 603965 A second gene associated with FSGS is TRPC6, which encodes a member of the canonical family of TRP channels. This family of ion channels conduct cations in a largely non-selective manner. As with ACTN4, TRPC6 is expressed in podocytes. While TRP channels can be activated through a variety of methods, TRPC6 is known to be activated by phospholipase C stimulation. There are at least 6 mutations in this channel, located throughout the channel. At least one of these mutations, P112Q, leads to increased intracellular calcium influx. It is unclear how this might lead to FSGS, though it has been proposed that it may result in alteration of podocyte dynamics or podocytopenia.[7]
FSGS3: CD2AP 607832 Another gene that may be involved in hereditary forms of FSGS is the gene known as CD2AP (CD2 associated protein) or CMS (Cas binding protein with multiple SH3 domains). The protein expressed by this gene is expressed in podocytes where it interacts with fyn and synaptopodin. There is a report that a splicing mutation in this gene was found in two patients with HIV associated FSGS and this led to altered protein translation. This has been theorized to result in altered actin binding and, thus, alteration of the cytoskeletal podocyte architecture.[7]
NPHS2 - Mutations in the NPHS2 gene, which codes for the protein called podocin,[8] can cause focal segmental glomerulosclerosis.[9] This is a recessive form of FSGS. An affected individual has two mutant copies of the NPHS2 gene, in contrast to ACTN4 and TRPC6 mediated forms of disease, which are dominant and require only one mutant copy of the gene. NPHS2-mediated FSGS is resistant to treatment with steroids.

Diagnosis

Symptoms and signs

In children and some adults, FSGS presents as a nephrotic syndrome, which is characterized by edema (associated with weight gain), hypoalbuminemia (low serum albumin, a protein in the blood), hyperlipidemia and hypertension (high blood pressure). In adults it may also present as kidney failure and proteinuria, without a full-blown nephrotic syndrome.

Tests

Differential diagnosis

Treatment

References

  1. ^ a b Kumar V, Fausto N, Abbas A (editors) (2003). Robbins & Cotran Pathologic Basis of Disease (7th ed.). Saunders. pp. 982–3. ISBN 978-0-721-60187-8.  
  2. ^ focal segmental glomerulosclerosis at Dorland's Medical Dictionary
  3. ^ "Renal Pathology". http://library.med.utah.edu/WebPath/RENAHTML/RENAL083.html. Retrieved 2008-11-25.  
  4. ^ "Focal_segmental_glomerulosclerosis of the Kidney". http://pathweb.uchc.edu/eAtlas/Code/1505.HTM. Retrieved 2008-11-25.  
  5. ^ "Focal_segmental_glomerulosclerosis of the Kidney". http://sites.google.com/site/medschoolnotesorg/pathology/kidney. Retrieved 2009-11-20.  
  6. ^ a b c Thomas DB, Franceschini N, Hogan SL, et al. (2006). "Clinical and pathologic characteristics of focal segmental glomerulosclerosis pathologic variants". Kidney Int. 69 (5): 920–6. doi:10.1038/sj.ki.5000160. PMID 16518352.  
  7. ^ a b c Mukerji N, Damodaran TV, Winn MP (2007). "TRPC6 and FSGS: The latest TRP channelopathy". Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease 1772: 859. doi:10.1016/j.bbadis.2007.03.005. PMID 17459670.  
  8. ^ Tsukaguchi H, Sudhakar A, Le TC, et al. (December 2002). "NPHS2 mutations in late-onset focal segmental glomerulosclerosis: R229Q is a common disease-associated allele". J. Clin. Invest. 110 (11): 1659–66. doi:10.1172/JCI16242. PMID 12464671.  
  9. ^ Franceschini N, North KE, Kopp JB, McKenzie L, Winkler C (February 2006). "NPHS2 gene, nephrotic syndrome and focal segmental glomerulosclerosis: a HuGE review". Genet. Med. 8 (2): 63–75. doi:10.1097/01.gim.0000200947.09626.1c. PMID 16481888. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?an=00125817-200602000-00001.  

External links

  • NephCure Foundation Only organization solely committed to support research seeking the cause of Nephrotic Syndrome and FSGS, improve treatment and find the cure.
  • Kidcomm An online resource for parents dealing with childhood kidney diseases (FSGS, Nephrotic Syndrome and others)
  • FSGS Research A team of kidney doctors and scientists from Brigham and Women's Hospital / Harvard Medical School working to learn more about the cause of FSGS and Nephrotic Syndrome in children and adults, with an emphasis on the genetic basis of these diseases.
  • [1] A general overview of Renal Pathology







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