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Reviewed September 2010

What is the official name of the CFI gene?

The official name of this gene is “complement factor I.”

CFI is the gene's official symbol. The CFI gene is also known by other names, listed below.

Read more about gene names and symbols on the About page.

What is the normal function of the CFI gene?

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.

Does the CFI gene share characteristics with other genes?

The CFI gene belongs to a family of genes called complement (complement system).

A gene family is a group of genes that share important characteristics. Classifying individual genes into families helps researchers describe how genes are related to each other. For more information, see What are gene families? in the Handbook.

How are changes in the CFI gene related to health conditions?

complement factor I deficiency - caused by mutations in the CFI gene

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.

other disorders - associated with the CFI gene

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.

Genetics Home Reference provides additional information about these conditions associated with changes in the CFI gene:

Where is the CFI gene located?

Cytogenetic Location: 4q25

Molecular Location on chromosome 4: base pairs 109,731,221 to 109,802,225

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBIThis link leads to a site outside Genetics Home Reference.)

The CFI gene is located on the long (q) arm of chromosome 4 at position 25.

The CFI gene is located on the long (q) arm of chromosome 4 at position 25.

More precisely, the CFI gene is located from base pair 109,731,221 to base pair 109,802,225 on chromosome 4.

See How do geneticists indicate the location of a gene? in the Handbook.

Where can I find additional information about CFI?

You and your healthcare professional may find the following resources about CFI helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the CFI gene or gene products?

  • AHUS3
  • C3B/C4B inactivator
  • C3BINA
  • C3b-INA
  • C3b-inactivator
  • complement component I
  • complement control protein factor I
  • complement factor I heavy chain
  • complement factor I preproprotein
  • FI
  • IF
  • KAF
  • Konglutinogen-activating factor
  • light chain of factor I

Where can I find general information about genes?

The Handbook provides basic information about genetics in clear language.

These links provide additional genetics resources that may be useful.

What glossary definitions help with understanding CFI?

atypical ; autoimmune ; bacteria ; complement protein ; deficiency ; expressed ; factor I ; gene ; immune response ; immune system ; inflammation ; kidney ; polymorphism ; protein ; proteinuria ; retina ; syndrome ; visual acuity

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.

See also Understanding Medical Terminology.

References (11 links)


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

Reviewed: September 2010
Published: February 8, 2016