Pathophysiology of minimal change nephrotic syndrome and focal segmental glomerulosclerosis.

Minimal change nephrotic syndrome (MCNS) is the most common cause of the nephrotic syndrome in children, accounting for 90% of cases under the age of 10 years and more than 50% in older children. It has been proposed that MCNS reflects a disorder of T-lymphocytes. These T cells are thought to release a cytokine - so-called permeability factor - that injures the glomerular epithelial cells. The identity of this permeability factor is still uncertain. Epithelial cell damage may lead to albuminuria in MCNS by altering the metabolism of polyanions, such as heparan sulphates, that constitute most of the normal charge barrier to the glomerular filtration of macromolecules such as albumin. In contrast, in focal segmental glomerulosclerosis (FSGS) the proteinuria is primarily due to an increased number of large pores in the glomerular basement membrane, leading to an impairment in size selectivity. It has been documented by repeated renal biopsies that some patients with apparent MCNS at the initial biopsy progress to FSGS. Morphological signs which have been proposed to identify the high-risk subset of MCNS include widespread IgM deposits (IgM nephropathy) and diffuse mesangial hypercellularity. It has been also documented that the initial biopsy of paediatric patients who subsequently showed FSGS had larger glomeruli from children with MCNS and healthy controls. Therefore, the presence of glomerular hypertrophy in biopsies of apparent MCNS appeared to be a high specific indicator of increased risk for progression to FSGS. In comparison with MCNS, a higher proportion of patients with mild mesangial hypercellularity are initial non-responder. More severe degree of mesangial hypercellularity, as seen in patients with diffuse mesangial hypercellularity, was associated with an even poorer initial response to steroid. Accordingly, it appears that mesangial proliferative glomerulonephritis is a more severe form of MCNS in which the initial injury is greater, leading to mesangial dysfunction and a slower rate of recovery, and this disorder is a part of the MCNS-FSGS spectrum. In this viewpoint, it can also be said that FSGS is the most severe form of MCNS in which the initial injury is the greatest, so the majority of patients with FSGS are non-responders to steroid and progress to chronic renal failure. In summary, documents define the risk for progressive renal disease based on the presence of mesangial hypercellularity and glomerular hypertrophy in renal biopsies of patients with MCNS, thus directing vigilant follow up and more aggressive treatment of high-risk patients.