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- C3 Glomerulopathy (C3G) is a rare disease caused by a fault in the complement system. Complement is part of your body’s normal immune response to bugs.
- Your body has an in-built system of protector proteins that stop complement from attacking your own cells. In C3G this system fails.
- This causes complement – primarily the complement protein C3 – to be deposited in a part of the kidney called the glomerular basement membrane.
- This leads to holes developing in the membrane and large protein molecules that are normally not excreted are able to leak out into the urine – this is known as proteinuria.
- Over time this proteinuria will damage the kidney and may lead to end stage kidney disease.
What are MPGN, C3GN, DDD?
- Membrano-Proliferative Glomerulonephritis (MPGN) refers to a group of diseases based on how the kidney looks under a microscope. In MPGN the kidney is damaged by deposits of immune substances in the glomerular basement membrane.
- These deposits can be immunoglobulins, complement or a mixture of both.
- Where the deposits are predominantly complement and are thought to be caused by abnormal activity in the complement system this is known as C3 Glomerulopathy.
- The terms C3 Glomerulonephritis (C3GN) and Dense Deposit Disease (DDD) are sub-groups of C3G and are distinguished by the way in which the complement deposits are seen on a biopsy.
– In C3GN the deposits tend to appear patchy.
– In DDD the deposits are seen more as long thick strips of complement.
Why does C3G happen?
- Patients may develop autoantibodies to the complement proteins. These autoantibodies then attack the protein and stop it from doing its job.
- There may also be a genetic fault in the complement system or the protector proteins that allows complement to be deposited in the kidney.
How does C3G present?
- C3G does not normally present acutely, symptoms normally develop over a period of months.
– Patients may notice haematuria (blood in the urine.)
– A urinalysis or urine dipstick may be performed, often for an unrelated reason such as a routine medical examination, which shows microscopic haematuria or proteinuria (protein in the urine).
– Patients may also complain of fluid and swelling in their lower limbs.
– In many cases a problem is not identified until a blood test shows abnormal kidney function and the patient is referred to a kidney specialist.