Minimal-change disease (MCD), also known as lipoid nephrosis or nil disease, is the most common single form of nephrotic syndrome in children. It refers to a histopathologic lesion in the glomerulus that almost always is associated with nephrotic syndrome. It typically is a disease of childhood, but it also can occur in adults.
It is postulated that MCD is a disorder of T cells, which release a cytokine that injures the glomerular epithelial foot processes. This, in turn, leads to a decreased synthesis of polyanions. The polyanions constitute the normal charge barrier to the filtration of macromolecules, such as albumin. When the polyanions are damaged, leakage of albumin follows. The identity of this circulating permeability factor is uncertain, although it is postulated that it may be hemopexin.
Some of the cytokines that have been studied in MCD are interleukin-12 (IL-12) and interleukin-4 (IL-4). IL-12 levels have been found to be elevated in peripheral blood monocytes during the active phase and normalized during remission. Interleukin-18 (IL-18) can synergize with IL-12 to selectively increase the production of vascular permeability factor from T cells. In addition, levels of IL-4 and CD23 (a receptor for immunoglobulin E [IgE]  ) have been found to be elevated in peripheral blood lymphocytes.
Synaptopodin is a proline-rich protein intimately associated with actin microfilaments present in the foot processes of podocytes. Greater synaptopodin expression in podocytes is associated with a significantly better response to steroid therapy. On the other hand, the expression of synaptopodin does not predict progression of MCD or diffuse mesangial hypercellularity to focal segmental glomerulosclerosis (FSGS). Thus, this marker could be used in the future to help determine appropriate therapy.
Interleukin-13 (IL-13) has been implicated in the pathogenesis of MCD. In a study on Chinese children in Singapore, it was shown that IL-13 genetic polymorphisms correlate with the long-term outcome of MCD. An animal study by Lai et al suggested that IL-13 overexpression can cause podocyte foot process fusion and proteinuria. 
In patients who develop acute renal failure, endothelin 1 expression is greater in the glomeruli, vessels, and tubules than in the nonacute renal failure group. The glomerular epithelial cells (podocytes) and the slit diaphragm connecting the podocyte foot processes play a primary role in the development of proteinuria.
Nephrin is a major component of the slit diaphragm. The slit diaphragm is often missing in MC nephrotic syndrome (MCD) kidneys. The role of nephrin and the slit diaphragm in MCD is not known. However, genetic variants of a glomerular filter protein may play a role in some patients with MCD.
Izzedine et al found a lack of glomerular dysferlin expression associated with minimal-change nephropathy in a patient with limb-girdle muscular dystrophy type 2B.  In the same study, 2 of 3 other patients with dysferlinopathy had microalbuminuria.
CD 80, a protein found in B cells and responsible for T-cell activation, is found to be increased in patients with MCD. However, the levels of this protein are not elevated in the urines of patients with FSGS compared with patients with MCD. Thus, this may have clinical applicability in distinguishing these two entities. 
In a study of 37 patients with MCD, 27 patients with FSGS, 30 patients with other glomerulopathies, and 71 healthy controls, Ling and colleagues found that urinary CD80 concentrations were significantly higher in patients with active MCD compared with patients with FSGS or other glomerulopathies and controls. At a cutoff value of 328.98 ng/g creatinine, urinary CD80 had a sensitivity of 81.1 % and a specificity of 94.4 % for diagnosing MCD. 
In preadolescents, minimal-change nephrotic syndrome (MCNS) makes up 85-95% of all cases of nephrotic syndrome. In adolescents and young adults, the prevalence is 50%, while in adults, MCNS accounts for 10-15% of primary nephrotic syndrome cases. The incidence of nephrotic syndrome is 2-7 new cases annually per 100,000 children, and the prevalence is 15 cases per 100,000 children.
Very few patients progress to end-stage renal disease. These patients are those who have FSGS that has been misdiagnosed as MCD.
Hypovolemic shock is perhaps the most serious complication of MCD. Hypovolemic shock typically occurs during the edema-forming phase of relapse and may be precipitated by diarrhea, sepsis, drainage of ascitic fluid, or the use of diuretics.
Thromboembolic events are serious complications of nephrotic syndrome. Peripheral thrombosis may result in gangrene, and deep venous thrombosis in the legs or pelvic veins may be a source of pulmonary emboli. Bacterial infections, especially peritonitis, occur with greater frequency, partly because of the loss of immunoglobulin G (IgG) and complement factors B and D in the urine. In fact, the largest reduction in mortality in these patients follows the introduction of antibiotics rather than any specific therapy.
Race-, Sex-, and Age-related Demographics
Rates of MCD vary as follows:
Asians may be at increased risk for MCD
In children, MCD is found twice as frequently in boys than in girls; in adults, however, the frequency is the same between the sexes
The incidence of MCD peaks in children aged 2 years, with approximately 80% being younger than 6 years at the time of diagnosis
In adults, the mean age of onset is 40 years
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