complement factor I
The CFI gene provides instructions for making a protein called complement factor I. This protein helps regulate a part of the body's immune response known as the complement system. The complement system is a group of proteins that work together to destroy foreign invaders (such as bacteria and viruses), trigger inflammation, and remove debris from cells and tissues. This system must be carefully regulated so it targets only unwanted materials and does not attack the body's healthy cells. Complement factor I and several related proteins protect healthy cells by preventing activation of the complement system when it is not needed.
At least 10 mutations in the CFI gene have been identified in people with complement factor I deficiency, a disorder characterized by immune system dysfunction. The mutations result in abnormal, nonfunctional, or absent complement factor I.
The lack (deficiency) of functional complement factor I protein allows uncontrolled activation of the complement system. The unregulated activity of the complement system decreases blood levels of another complement protein called C3, reducing the immune system's ability to fight infections. In addition, the immune system may malfunction and attack its own tissues, resulting in autoimmune disorders.
Genetics Home Reference provides information about age-related macular degeneration.
Genetics Home Reference provides information about atypical hemolytic-uremic syndrome.
Genetics Home Reference provides information about C3 glomerulopathy.
Mutations in the CFI gene have also been found in people with glomerulonephritis with isolated C3 deposits. This condition, which may also occur in people with complement factor I deficiency, is characterized by kidney malfunction that can be serious or life-threatening. The CFI gene mutations identified in this disorder result in an abnormal or nonfunctional version of complement factor I. The defective protein allows uncontrolled activation of the complement system. The overactive complement system attacks certain kidney cells, which damages the kidneys and leads to a loss of protein in the urine (proteinuria).
A common variation (polymorphism) in the CFI gene has also been associated with age-related macular degeneration (AMD). AMD is a leading cause of vision loss among the elderly. It is characterized by damage to the retina and a loss of sharp vision (visual acuity). Researchers suggest that the CFI gene variation that has been associated with AMD changes the way the gene is activated (expressed). It is unclear how this change is related to the development of AMD. A combination of genetic and environmental factors likely determines the risk of developing this complex eye disorder.
- C3B/C4B inactivator
- complement component I
- complement control protein factor I
- complement factor I heavy chain
- complement factor I preproprotein
- Konglutinogen-activating factor
- light chain of factor I