MPGN (Membranoproliferative Glomerulonephritis Type 1, sometimes known as Mesangiocapillary Glomerulonephritis or MCGN), DDD (Dense Deposit Disease, previously called MPGN Type II) and C3G (C3 Glomerulopathy) are related diseases which damage the kidneys. These diseases are very rare and are characterised by dysfunction of the immune system.
Healthy kidneys contain millions of filtering units called nephrons, which remove waste products from the blood. Inside each nephron is a glomerulus (looks rather like a cup). When the glomeruli become inflamed as a result of attack by the immune system, the filtering process is impaired and the kidneys become less able to carry out their job. Consequently, substances such as protein and blood can leak into the urine.
The Immune System
Normally the various parts of the immune system (mostly antibodies and complement, which are very important chemicals circulating round the body) work together to recognise, signal the presence of and destroy invading germs. However, in MPGN/DDD/C3G the recognition and signalling systems get confused and the immune system attacks the healthy kidneys.
Your doctor will usually determine the type of disease you have by carrying out a kidney biopsy. This is when a small sample of tissue is taken from the kidney and examined under an electron microscope. It can sometimes take a little while for the specific type of disease to be identified.
MPGN Type 1
In MPGN, complement and antibodies are present in the glomeruli. They should not be there and they can cause damage to the affected area.
DDD
DDD is identified by the appearance of dense patches of complement in the kidney biopsy (hence the name dense deposit) and some other unknown substances, but no antibodies.
C3G
C3G gets its name from the complement C3 deposits which are usually found in the kidney biopsy. There are no antibodies.
What does the future hold?
The cause of these diseases and how they work is not yet fully understood, and there are no truly effective treatments currently on the market. However, much research is being undertaken and development of more effective treatments is under way. Promising new drugs are on the horizon as researchers work to find a cure for these difficult diseases.
For more detailed information on these rare diseases, as well as up-to-date news on the Rare Renal Working Group visit: http://rarerenal.org/patient-information/mpgn-ddd