Learn how C3G and primary IC-MPGN are diagnosed, what tests are used, and how these rare kidney diseases typically progress over time.
What are C3G and primary IC-MPGN?
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Living with a rare kidney disease such as C3 glomerulopathy (C3G) or primary (idiopathic) immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) can feel overwhelming. This guide is designed to help you better understand your diagnosis and empower you to confidently discuss your needs and care plan with your healthcare team.
2025-09-18
NP-39591
C3G and primary IC-MPGN are two different ultra-rare kidney diseases that share a common issue: an overactive C3 protein in the immune system. Normally, C3 helps protect the body from infections, but when it becomes overactive, it can mistakenly damage the kidneys. This happens by affecting the glomeruli—the tiny filters in the kidneys responsible for removing waste and excess fluid.
Despite being distinct conditions, C3G and primary IC-MPGN have overlapping symptoms, including the triad of:1
- Proteinuria (high levels of protein in the urine)
- Reduced kidney function
- C3 deposits in the kidney
While C3G and primary IC-MPGN are similar, they are caused by different underlying processes
in the body. Finding these differences in a biopsy helps your doctor provide an accurate diagnosis so that together you can choose the best care plan for you.
About 1 to 3 new cases of C3G are diagnosed each year for every one million people worldwide, and primary IC-MPGN may be even rarer.2
C3G1,3
C3G occurs when an abnormal amount of the C3 protein is found in the kidneys without
significant antibody involvement.
Primary IC-MPGN1,4
Primary IC-MPGN occurs when both C3 and antibodies build up in the kidneys.
Diagnosis and progression
1 Bomback, A.S., Charu, V., and Fakhouri, F. (2025) Challenges in the Diagnosis and Management of Immune Complex-Mediated Membranoproliferative Glomerulonephritis and Complement 3 Glomerulopathy. Kidney International Reports, 10(1), pp. 17-28.
2 Orphanet (2024). C3 glomerulopathy. Available at: www.orpha.net/en/disease/detail/329918
3 Caravaca-Fontán, F., Lucientes, L., Cavero, T., and Praga, M. (2020). Update on C3 Glomerulopathy: A Complement-Mediated Disease, Nephron, 144(6), pp. 272–280.
4 Noris, M., Donadelli, R. & Remuzzi, G. (2019). Autoimmune abnormalities of the alternative complement pathway in membranoproliferative glomerulonephritis and C3 glomerulopathy. Pediatr Nephrol, 34, pp. 1311–1323 (2019).