What is C3 glomerulopathy (C3G)?
C3 glomerulopathy (C3G) is an immune system disorder that causes damage to the tiny filters in the kidney (glomeruli). It occurs when part of the immune system called complement C3 is deposited in the kidneys. This affects the kidneys’ ability to filter the blood and can eventually lead to a reduction of kidney function.
C3G is a subtype of a condition called membranoproliferative glomerulonephritis (MPGN). There is also a specific type of C3G called dense deposit disease (DDD). These conditions are dealt with separately.
The precise diagnosis depends on the exact location and appearance of the C3 deposits in the kidneys.
C3G was only recognised as a distinct condition in 2013 so research is still in its early stages.
C3G affects around 1 in 500,000 people in the UK. Men and women are affected equally.
What are the signs and symptoms of C3G?
Some people with C3G do not have any symptoms and the condition is found after a routine blood test shows a drop in kidney function.
When symptoms do occur, they include:
- Blood in the urine (haematuria) – the urine may look red or dark brown (like a cola drink). This is more likely to be noticed after an infection such as a cold or sore throat, and usually fades after a few days. The blood may be invisible to the naked eye and only seen under a microscope when the urine is tested (microscopic haematuria). It does not cause any pain. The amount of blood in the urine is not an indication of how severe the condition is – more is not necessarily worse.
- Protein in the urine (proteinuria) – this is likely to only be seen under a microscope but if there a lot of protein, the urine may look frothy. The more protein there is in the urine, the more severe the condition is. If a later urine test shows lower levels of protein, this is a sign of improvement.
- Swelling or puffiness (oedema) – this can develop in different parts of the body, especially around the eyes and ankles. Swelling around the eyes tends to be worse first thing in the morning and improve as the day goes on, whereas ankle swelling is usually worse in the evenings. There is no pain associated with the swelling. It is not an allergic reaction but is caused by the kidneys retaining too much water.
- High blood pressure – this can damage the structure of the kidney if it is not treated.
C3G progresses at different rates for different people. If kidney failure occurs, dialysis and/or a transplant may be needed.
What causes C3G?
C3G is an autoimmune condition that occurs due to a fault in the body’s immune system. This causes a substance called complement C3 to be deposited in the kidneys. Complement normally works with antibodies to target and get rid of infections. When it is deposited in the kidneys, it can build up to damage the tiny filters (glomeruli) that normally filter the blood. This makes the filters leak protein and blood into the urine. Over time, this leads to a reduction in kidney function and eventual kidney damage.
How is C3G diagnosed?
CG3 is diagnosed by a kidney biopsy. This can show the precise diagnosis as well as how much damage has already been done to the kidneys.
The complement deposits look patchy when examined under a microscope after a biopsy.
Blood tests can check complement levels and genetic testing may be offered.
Does C3G affect other parts of the body?
C3 glomerulopathy is only known to affect the kidneys.
Does C3G run in families?
Recent research has found genetic abnormalities in around one in four people with C3G, but it is not yet known if or how these variations cause the condition.
Most cases of C3G are not inherited and occur with no family history of the condition.
How is C3G treated?
Treatment focuses on reducing blood pressure with medications known as angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs). These medications also help to reduce the loss of protein in the urine. This slows the progress of C3G and prevents, or at least delays, further kidney damage.
Immunosuppressants such as steroids may also be prescribed to help suppress the immune system.
Dietary changes may be recommended, including following a low-salt diet to reduce swelling.
A diuretic medication may be prescribed. These work by making the kidneys get rid of excess water and salt so they do not build up in the body and cause swelling. Vitamin D supplements may also be recommended if kidney function continues to decline. Any dietary changes should only be undertaken with advice and monitoring by a specialised kidney dietitian.
Dialysis and/or transplant may be needed if kidney damage becomes severe. C3G can reoccur in the transplanted kidney.
Where can I get more information or support about C3G?
For more information on C3G, including its diagnosis, symptoms and treatment, visit the MPGN/DDD Support Group.
Publication date: 11/2023
Review date: 11/2026
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