Focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis
Light micrograph of focal segmental glomerulosclerosis, hilar variant. Kidney biopsy. PAS stain.
Classification and external resources
Specialty
ICD-10	N00-N08 (with .1 suffix)
ICD-9-CM	581.1
OMIM	603278 603965 607832 612551 613237 600995
MedlinePlus	000478
eMedicine	med/2944
Patient UK	Focal segmental glomerulosclerosis
MeSH	D005923

Focal segmental glomerulosclerosis (FSGS) is a cause of nephrotic syndrome in children and adolescents, as well as a leading cause of kidney failure in adults. It is also known as "focal glomerular sclerosis" or "focal nodular glomerulosclerosis." It accounts for about a sixth of the cases of nephrotic syndrome. (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.)

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 each glomerulus is involved (as opposed to global), 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 immunoglobulin M (IgM) and C3-convertase (C3) in the sclerotic segment.

Classification

Depending on the cause it is broadly classified as:

• Primary, when no underlying cause is found; usually presents as nephrotic syndrome
• Secondary, when an underlying cause is identified; usually presents with kidney failure and proteinuria. This is actually a heterogeneous group including numerous causes such as
  • Infections such as HIV (known as HIV-Associated Nephropathy)
  • Toxins and drugs such as heroin and pamidronate
  • Familial forms
  • Secondary to nephron loss and hyperfiltration, such as with chronic pyelonephritis and reflux, morbid obesity, diabetes mellitus

There are many other classification schemes also.

Pathologic variants

Micrograph of the collapsing variant of FSGS (collapsing glomerulopathy). A collapsed glomerulus is seen at the top, right-of-centre. PAS stain. Kidney biopsy.

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

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. 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. Collapsing variant is most common type of glomerulopathy caused by HIV infection.

Causes

Some general secondary causes are listed below:

• Glomerular hypertrophy/hyperfiltration
  • Unilateral renal agenesis
  • Morbid obesity
• Scarring due to previous injury
  • Focal proliferative glomerulonephritis
  • Vasculitis
  • Lupus
• Toxins (pamidronate)
• Human immunodeficiency virus-associated nephropathy
• Heroin nephropathy

Focal segmental glomerulosclerosis may develop following acquired loss of nephron's from reflux nephropathy.Proteinuria is nonselective in most cases and may be in subnephrotic range(nephritic range <3.0gm/24hr) or nephritic range.

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.
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.
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.
FSGS4: APOL1	612551	In people of African descent, two common variants in APOL1 have been associated with FSGS. It is believed that these variants arose as a defensive mechanism against Trypanosoma brucei rhodesiense or some other sub-Saharan parasite despite conferring high susceptibility to FSGS when inherited from both parents.
FSGS5: INF2	613237	Another gene associated with FSGS is INF2, which encodes a member of the formin family of actin-regulating proteins. The observation that alterations in this podocyte-expressed formin cause FSGS emphasizes the importance of fine regulation of actin polymerization in podocyte function.
SRN1: NPHS2	600995	Mutations in the NPHS2 gene, which codes for the protein called podocin, can cause focal segmental glomerulosclerosis. 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.

Some researchers found SuPAR as a cause of FSGS.

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

• Urinalysis
• Blood tests — cholesterol
• Kidney biopsy

Differential diagnosis

• Minimal change disease, especially in children
• Membranous glomerulonephritis
• Several others

Treatment

• Salt restriction and diuretics, such as furosemide, for edema.
• Antihypertensives (especially ACEIs) — if the blood pressure is too high but not so for it, it has another protective effect
• Treat present hyperlipidemia (e.g. statins, fibrates; although fibrates are contraindicated in renal failure)
• Aldosterone antagonist to decrease proteinuria and thus offer a degree of reno-protection
• Angiotensin II receptor antagonist
• Rituximab
• Galactose
• Pirfenidone
• Tacrolimus
• Abatacept
• Corticosteroids, such as prednisone — based on the clinical judgment of physician (no broad consensus/guideline)
• Cytotoxics, such as cyclophosphamide may be used to induce remission in patients presenting with FSGS refractory to corticosteroids, or in patients who do not tolerate steroids.
• Plasmapheresis — blood cleansing using a machine to remove the patient's blood plasma and replacing it with donor plasma.
• Vitamin E
• Fish oil
• Immunosuppressive drugs
• If none of the above works, the patient will require dialysis with possibly later transplantation of a new kidney that probably will be lost fast by FSGS due the FSGS aggressor agent on the blood.

Notable patients

• Former NBA basketball players Sean Elliott and Alonzo Mourning have both survived bouts with FSGS. Mourning is an Ambassador to The NephCure Foundation. Pro bodybuilder Flex Wheeler was diagnosed with FSGS and had a kidney transplant. Former MLS player Clyde Simms retired from professional soccer in 2014 due to FSGS.
• Gary Coleman American actor, known for his childhood role as Arnold Jackson in the American sitcom Diff'rent Strokes.
• Andy Cole, former Newcastle Utd, Manchester United and England international football player
• Ed Hearn, former Major League Baseball player for the New York Mets and Kansas City Royals
• Aries Merritt, 110 metres hurdles world record holder and 2012 Olympic champion, had a kidney transplant for collapsing FSGS days after coming third in the 2015 World Championships.

See also

• Glomerulonephritis
• Nephrotic syndrome
• HMOX1

External links

• 01 - FSGS cure on 4 months with cheap no side effects LDN

02 - FSGS cure on 4 months with cheap no side effects LDN

• 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.
• A general overview of Renal Pathology