C3

MedlinePlus Genetics provides information about Atypical hemolytic-uremic syndrome

At least one mutation in the C3 gene has been found to cause a rare form of kidney disease called C3 glomerulopathy. This disorder damages the kidneys and can lead to end-stage renal disease (ESRD), a life-threatening condition that prevents the kidneys from filtering fluids and waste products from the body effectively.

The identified C3 gene mutation deletes two amino acids from the C3 protein. This genetic change is described as a "gain-of-function" mutation because it leads to an altered version of the protein that overactivates the complement system. The overactive system damages structures in the kidneys called glomeruli, which are clusters of tiny blood vessels that help filter waste products from the blood. Damage to glomeruli prevents the kidneys from filtering waste products normally and can lead to ESRD.

Several other changes in the C3 gene do not cause C3 glomerulopathy directly but appear to increase the likelihood of developing the disorder. In particular, the C3F allotype is seen more frequently in people with this condition than in the general population. Researchers are working to determine how the C3F allotype may influence disease risk.

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At least 17 mutations in the C3 gene have been found to cause C3 deficiency, a rare condition characterized by recurrent bacterial infections beginning in childhood. The genetic changes that cause C3 deficiency lead to an altered version of the C3 protein or prevent cells from producing any of this protein. These mutations are described as "loss-of-function" because the abnormal or missing C3 protein prevents normal activation of the complement system. As a result, the immune system is less able to protect the body against foreign invaders (such as bacteria).