C3 Glomerulopathy: Dense Deposit Disease and C3 Glomerulonephritis
National Organization for Rare Disorders, Inc.
It is possible that the main title of the report C3 Glomerulopathy: Dense Deposit Disease and C3 Glomerulonephritis is not the name you expected.
Over the past decade, important advances in our understanding of complement-mediated renal diseases have led to the adoption of new names or ‘disease categories' to more precisely group diseases that appear to share a similar cause. Consider, for example, dense deposit disease (DDD), a very rare kidney disease characterized on a renal biopsy test called ‘immunofluorescence' by an abundance of a protein called C3 in the renal glomeruli, and named for the extremely dense ‘sausage-like' deposits that are seen in the glomerular basement membrane (GBM) using electron microscopy. In 2013, as a result of a consensus meeting, scientists recommended that DDD be sub-grouped under a new heading – C3 Glomerulopathy, abbreviated C3G. The adoption of this new term was driven by the recognition that there is another group of patients with glomerular disease whose kidney biopsy is reminiscent of DDD. On electron microscopy, the deposits in these patients are lighter in color and more widespread in location, but on immunofluorescence, as with DDD there is an abundance of C3 in the renal glomeruli. These patients are said to have C3 glomerulonephritis or C3GN. In recognition of shared similarities, both DDD and C3GN are now classified as sub-types of C3G.
What happens in C3G? Recall that the glomeruli are the filtering units of the kidney, where blood gets filtered under pressure through the GBM into another space, called Bowman's space, as urine. About half a million glomeruli in each kidney do the filtering, creating a filtrate of water, sodium, potassium, chloride, glucose and small proteins. In both DDD and C3GN, deposits of C3 and other proteins in the GBM disrupt kidney function. Progressive damage to the glomeruli occurs and after about 10 years, enough damage has occurred so that about half of all persons with C3G have kidney failure. When kidney failure occurs, dialysis must be started or transplantation must be performed. The rate of progression to end-stage kidney failure and dialysis appears to be similar for both DDD and C3GN.
In addition to dense deposits in the kidney, persons with DDD can develop deposits in their eyes in an area called Bruch's membrane. This occurs because the ‘choriocapillaris-Bruch's membrane-retinal pigment epithelium' interface in the eye is very similar to the capillary-GBM interface in the kidney. The eye deposits are called drusen. Whether they occur more or less frequently in patients with C3GN is not clear.
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Last Updated: 9/15/2015
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