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Focal Segmental Glomerulosclerosis (FSG)
Focal segmental glomerulosclerosis (FSGS) is a disease in which scar tissue develops on the glomeruli, the small parts of the kidneys that filter waste from the blood.
One of the commonest cause of nephrotic syndrome and is characterized by the presence of focal (only some glomeruli are affected) and segmental (only a part of the glomerulus is affected) sclerosis of the glomeruli.
Types of FSGS include:
- Primary FSGS. -FSGS have no known cause for their condition. This is called primary (idiopathic) FSGS.
- Secondary FSGS.-Several factors, such as infection, drug toxicity, diseases including diabetes or sickle cell disease, obesity, and even other kidney diseases can cause secondary FSGS.
- Genetic FSGS.-This is a rare form of FSGS caused by genetic changes. It is also called familial FSGS. It's suspected when several members of a family show signs of FSGS. Familial FSGS can also occur when neither parent has the disease but each one carries a copy of an altered gene that can be passed on to the next generation.
- Unknown FSGS. - In some cases, the underlying cause of FSGS cannot be determined despite the evaluation of clinical symptoms and extensive testing.
Causes
- Idiopathic
- Secondary:
- Associated with loss of renal tissue as unilateral renal agenesis or advanced stages of reflux nephropathy or hypertensive nephropathy.
- Associated with conditions like Sickle cell anemia, HIV infection, Heroin abuse,Obesity.
- Inherited due to mutations in genes like nephrin, podocin and a-actinin 4.
Features
- Degeneration and focal disruption of the visceral epithelial cells is the hallmark feature of focal segmental glomerulosclerosis.
- The hyalinosis and sclerosis are due to protein entrapment.
- Mutation of the protein podocin and α-actinin 4 results in the development of autosomal recessive and autosomal dominant forms of focal segmental glomerulosclerosis respectively.
Microscopy
- Light microscopy reveals the focal segmental sclerosis and hyalinization of the glomeruli.
- Electron microscopy demonstrates the diffuse effacement of the podocytes, focal detachment of the epithelial cells and increased mesangial matrix in the sclerotic areas.
- Five mutually exclusive variants of FSGS may be distinguished by the
pathological findings seen on renal biopsy
- Collapsing variant
- Glomerular tip lesion variant
- Cellular variant
- Perihilar variant
- Not otherwise specified variant (NOS)
Immunofluorescence
- It demonstrates C3 and IgM deposits in the sclerotic areas and the mesangium
It affects all age groups and is characterized by the clinical features of nonselective proteinuria, reduction in GFR and presence of hypertension and poor response to corticosteroids.
There is high incidence of recurrence in transplant patients.
Children have better prognosis than adults.
