C2 gene

At least five mutations in the C2 gene have been found to cause complement component 2 deficiency. This disorder reduces the normal function of the immune system, resulting in an increased risk for infections and autoimmune disorders such as systemic lupus erythematosus (SLE). Autoimmune disorders occur when the immune system malfunctions and attacks the body's tissues and organs.

More than 90 percent of people with complement component 2 deficiency have a mutation that deletes 28 DNA building blocks (nucleotides) from the C2 gene. This mutation prevents the production of any complement component 2 protein. Without this protein to form C3 convertase, activation of the complement system is stalled. As a result, the complement system's ability to fight infections is diminished. It is unclear how complement component 2 deficiency leads to increased susceptibility to autoimmune disorders. Researchers speculate that the dysfunctional complement system is unable to distinguish what it should attack, and it sometimes attacks normal tissues, leading to autoimmunity. Alternatively, the dysfunctional complement system may perform partial attacks on invading molecules, which leaves behind foreign fragments that are difficult to distinguish from the body's tissues, so the complement system sometimes attacks the body's own cells. It is likely that other factors, both genetic and environmental, play a role in the variability of the signs and symptoms of complement component 2 deficiency.

MedlinePlus Genetics provides information about Age-related macular degeneration