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.)

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.

The histopathology is characterized by interstitial fibrosis, tubular atrophy,

fibrotic intimal thickening of arteries and glomerulosclerosis.

CAN is characterized by a gradual decline in kidney function and, typically, accompanied by high blood pressure and hematuria.

Ask-Upmark kidneys are a cause of secondary hypertension that can be curable.

Renal segmental hypoplasia, also Ask-Upmark kidney, is a kidney with a partially developed or atrophic renal cortex.

The most common malformation in patients with the syndrome is kidney hypodysplasia, which are small and underdeveloped kidneys, often leading to end-stage renal disease (ESRD). Estimates show approximately 10% of children with hypoplastic kidneys are linked to the disease. Many different histological abnormalities have been noted, including:

- decrease in nephron number associated with hypertrophy

- focal segmental glomerulosclerosis

- interstitial fibrosis and tubular atrophy

- multicystic dysplastic kidney

Up to one-third of diagnosed patients develop end stage kidney disease, which may lead to complete kidney failure.

Diffuse proliferative nephritis (DPN) or glomerulonephritis (DPGN) is a type of glomerulonephritis that is the most serious form of renal lesions in SLE and is also the most common, occurring in 35% to 60% of patients. Most of the glomeruli show endothelial and mesangial proliferation affecting the entire glomerulus, leading to diffuse hypercellularity of the glomeruli, producing in some cases epithelial crescents that fill Bowman's space. When extensive, immune complexes create an overall thickening of the capillary wall, resembling rigid "wire loops" on routine light microscopy. Electron microscopy reveals electron-dense subendothelial immune complexes (between endothelium and basement membrane). Immune complexes can be visualized by staining with fluorescent antibodies directed against immunoglobulins or complement, resulting in a granular fluorescent staining pattern. In due course, glomerular injury gives rise to scarring (glomerulosclerosis). Most of these patients have hematuria with moderate to severe proteinuria, hypertension, and renal insufficiency.

Transplant glomerulopathy, abbreviated TG, is a disease of the glomeruli in transplanted kidneys. It is a type of renal injury often associated with chronic antibody-mediated rejection. However, transplant glomerulopathy is not specific for chronic antibody-mediated rejection; it may be the result of a number of disease processes affecting the glomerular endothelium.

Ocular disc dysplasia is the most notable ocular defect of the disease. An abnormal development in the optic stalk causes optic disc dysplasia, which is caused by a mutation in the "Pax2" gene. The nerve head typically resembles the morning glory disc anomaly, but has also been described as a coloboma. A coloboma is the failure to close the choroid fissure, which is the opening from the ventral side of the retina in the optic stalk. Despite the similarities with coloboma and morning glory anomaly, significant differences exist such that optic disc dysplasia cannot be classified as either one entity.

Optic disc dysplasia is noted by an ill-defined inferior excavation, convoluted origin of the superior retinal vessels, excessive number of vessels, infrapapillary pigmentary disturbance, and slight band of retinal elevation adjacent to the disk. Some patients have normal or near normal vision, but others have visual impairment associated with the disease, though it is not certain if this is due only to the dysplastic optic nerves, or a possible contribution from macular and retinal malformations. The retinal vessels are abnormal or absent, in some cases having small vessels exiting the periphery of the disc. There is a great deal of clinical variability.

Diffuse leiomyomatosis of the esophagus and tracheobronchial tree has been reported in some families with Alport syndrome. Symptoms usually appear in late childhood and include dysphagia, postprandial vomiting, substernal or epigastric pain, recurrent bronchitis, dyspnea, cough, and stridor. Leiomyomatosis is confirmed by computed tomography (CT) scanning or magnetic resonance imaging (MRI).

HIV-associated nephropathy (HIVAN) refers to kidney disease developing in association with HIV infection. The most common, or "classical", type of HIV-associated nephropathy is a collapsing focal segmental glomerulosclerosis (FSGS), though other forms of kidney disease may also occur with HIV. Regardless of the underlying histology, renal disease in HIV-positive patients is associated with an increased risk of death.

HIVAN may be caused by direct infection of the renal cells with the HIV-1 virus, with resulting renal damage through the viral gene products. It could also be caused by changes in the release of cytokines during HIV infection. Usually occurs only in advanced disease and approximately 80% of patients with HIVAN have a CD4 count of less than 200. HIVAN presents with nephrotic syndrome and progressive kidney failure. Despite being a cause of chronic kidney failure, kidney sizes are usually normal or large.

Various eye abnormalities are often seen including lenticonus, keratoconus, cataracts as well as retinal flecks in the macula and mid-periphery. These rarely threaten vision. Lenticonus (cone-shaped lens) can be treated by replacement of the lens, as for cataracts. Mild keratoconus can be treated with hard or piggy-back contact lenses; severe cases may require a corneal transplant.

HIVAN is the third most common cause of ESRF among African Americans, and commonly seen in African-American patients with HIV compared with other ethnic groups. In the USA 12% of patients dying with AIDS have histologically proven HIVAN, the worldwide incidence amongst AIDS patients appears to be similar. A South African study at Tygerberg Hospital, Stellenbosch University, has shown HIVAN histology in 33/61(54%) biopsies performed in HIV positive patients.

Membranous glomerulonephropathy (MGN) is a slowly progressive disease of the kidney affecting mostly people between ages of 30 and 50 years, usually Caucasian.

It is the second most common cause of nephrotic syndrome in adults, with focal segmental glomerulosclerosis (FSGS) recently becoming the most common.

Cutis marmorata also occurs in decompression sickness (DCS). Although it is considered Type I DCS, which is non-neurological, it is typically treated as if the patient has the more severe Type II DCS. This is because past experience in diving medicine has shown that patients initially presented with only this symptom have a high likelihood of progression to neurological, Type II, DCS without prompt treatment. The marbling does not resolve until few days after treatment, but any pruritus (itching) will likely disappear upon initial recompression.

The closely related terms membranous nephropathy and membranous glomerulopathy both refer to a similar constellation but without the assumption of inflammation.

Membranous nephritis (in which inflammation is implied, but the glomerulus not explicitly mentioned) is less common, but the phrase is occasionally encountered. These conditions are usually considered together.

By contrast, membranoproliferative glomerulonephritis has a similar name, but is considered a separate condition with a distinctly different causality. Membranoproliferative glomerulonephritis involves the basement membrane and mesangium, while membranous glomerulonephritis involves the basement membrane but not the mesangium. (Membranoproliferative glomerulonephritis has the alternate name "mesangiocapillary hohki", to emphasize its mesangial character.)

It is characterized by glomerular basement membrane thickening (referred to as "tram-tracking of the basement membrane"), increased mesangial matrix and segmental and global glomerulosclerosis.

The differential diagnosis of tram-tracking includes membranoproliferative glomerulonephritis (especially hepatitis C), and thrombotic microangiopathies.

More specifically, glomerulosclerosis can refer to:

- Focal segmental glomerulosclerosis

- Nodular glomerulosclerosis (diabetic)

Minimal change disease is characterised as a cause of nephrotic syndrome without visible changes in the glomerulus on microscopy. Minimal change disease typically presents with edema, an increase in proteins passed from urine and decrease in blood protein levels, and an increase in circulating lipids (i.e., nephrotic syndrome) and is the most common cause of the nephrotic syndrome in children. Although no changes may be visible by light microscopy, changes on electron microscopy within the glomerules may show a fusion of the foot processes of the podocytes (cells lining the basement membrane of the capillaries of glomerulus). It is typically managed with corticosteroids and does not progress to chronic kidney disease.

Phakomatosis pigmentokeratotica is a rare neurocutanous condition characterized by the combination of an organoid sebaceous nevus and speckled lentiginous nevus. It is an unusual variant of epidermal naevus syndrome. It was first described by Happle "et al". It is often associated with neurological or skeletal anomalies such as hemiatrophy, dysaesthesia and hyperhidrosis in a segmental pattern, mild mental retardation, seizures, deafness, ptosis and strabismus.

Focal segmental glomerulosclerosis is characterised by a sclerosis of segments of some glomerules. It is likely to present as a nephrotic syndrome. This form of glomerulonephritis may be associated with conditions such as HIV and heroin abuse, or inherited as Alport syndrome. The cause of about 20–30% of focal-segmental glomerulosclerosis is unknown. On microscopy, affected glomerules may show an increase in hyalin, a pink and homogenous material, fat cells, an increase in the mesangial matrix and collagen. Treatment may involve corticosteroids, but up to half of people with focal segmental glomerulonephritis continue to have progressive deterioration of kidney function, ending in kidney failure.

Livedoid vasculopathy (also known as "livedoid vasculitis", "livedo reticularis with summer/winter ulceration" and "segmental hyalinizing vasculitis") is a chronic cutaneous disease seen predominantly in young to middle-aged women. One synonym used to describe its features is "Painful purpuric ulcers with pattern of the lower extremities" (PURPLE).

It can be divided into a primary (or idiopathic) form and a secondary form, which has been associated with a number of diseases, including chronic venous hypertension and varicosities.

When a newborn infant is exposed to low environmental temperatures, an evanescent, lacy, reticulated red and/or blue cutaneous vascular pattern appears over most of the body surface. This vascular change represents an accentuated physiologic vasomotor response that disappears with increasing age, although it is sometimes discernible even in older children.

Persistent and pronounced cutis marmorata occurs in Menke's disease, familial dysautonomia, Cornelia de Lange, trisomy 13 and trisomy 18 syndromes.

Also seen in Cardiogenic Shock.

Cutis marmorata telangiectatica congenita is clinically similar, but the lesions are more intense, may be segmental, are persistent, and may be associated with loss of dermal tissue, epidermal atrophy and ulceration.

Frasier syndrome presents at birth with male pseudohermaphroditism (the external genitalia have a female appearance despite an XY genotype), streak gonads and progressive glomerulonephropathy (focal segmental glomerulosclerosis). Patients are also at increased risk of genito-urinary tumors (usually gonadoblastoma).

The glomerulonephropathy presents later than in Denys-Drash syndrome, and the tumour risk phenotype is different; whilst Denys-Drash syndrome is associated with Wilms' tumour, Frasier syndrome is associated with gonadoblastoma. Differentiating between the two syndromes can be challenging.