Skip Navigation
Genetics Home Reference: your guide to understanding genetic conditions About   Site Map   Contact Us
Home A service of the U.S. National Library of Medicine®
Printer-friendly version
Complement component 2 deficiency

Complement component 2 deficiency

Reviewed June 2014

What is complement component 2 deficiency?

Complement component 2 deficiency is a disorder that causes the immune system to malfunction, resulting in a form of immunodeficiency. Immunodeficiencies are conditions in which the immune system is not able to protect the body effectively from foreign invaders such as bacteria and viruses. People with complement component 2 deficiency have a significantly increased risk of recurrent bacterial infections, specifically of the lungs (pneumonia), the membrane covering the brain and spinal cord (meningitis), and the blood (sepsis), which may be life-threatening. These infections most commonly occur in infancy and childhood and become less frequent in adolescence and adulthood.

Complement component 2 deficiency is also associated with an increased risk of developing autoimmune disorders such as systemic lupus erythematosus (SLE) or vasculitis. Autoimmune disorders occur when the immune system malfunctions and attacks the body's tissues and organs. Between 10 and 20 percent of individuals with complement component 2 deficiency develop SLE. Females with complement component 2 deficiency are more likely to have SLE than affected males, but this is also true of SLE in the general population.

The severity of complement component 2 deficiency varies widely. While some affected individuals experience recurrent infections and other immune system difficulties, others do not have any health problems related to the disorder.

How common is complement component 2 deficiency?

In Western countries, complement component 2 deficiency is estimated to affect 1 in 20,000 individuals; its prevalence in other areas of the world is unknown.

What genes are related to complement component 2 deficiency?

Complement component 2 deficiency is caused by mutations in the C2 gene. This gene provides instructions for making the complement component 2 protein, which 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, trigger inflammation, and remove debris from cells and tissues. The complement component 2 protein is involved in the pathway that turns on (activates) the complement system when foreign invaders, such as bacteria, are detected.

The most common C2 gene mutation, which is found in more than 90 percent of people with complement component 2 deficiency, prevents the production of complement component 2 protein. A lack of this protein impairs activation of the complement pathway. As a result, the complement system's ability to fight infections is diminished. It is unclear how complement component 2 deficiency leads to an increase in 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.

Read more about the C2 gene.

How do people inherit complement component 2 deficiency?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Where can I find information about diagnosis or management of complement component 2 deficiency?

These resources address the diagnosis or management of complement component 2 deficiency and may include treatment providers.

You might also find information on the diagnosis or management of complement component 2 deficiency in Educational resources and Patient support.

General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.

To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.

Where can I find additional information about complement component 2 deficiency?

You may find the following resources about complement component 2 deficiency helpful. These materials are written for the general public.

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

What other names do people use for complement component 2 deficiency?

  • C2D
  • C2 deficiency
  • complement 2 deficiency

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines and How are genetic conditions and genes named? in the Handbook.

What if I still have specific questions about complement component 2 deficiency?

Where can I find general information about genetic conditions?

What glossary definitions help with understanding complement component 2 deficiency?

autoimmune ; autoimmunity ; autosomal ; autosomal recessive ; bacteria ; cell ; deficiency ; gene ; immune response ; immune system ; immunodeficiency ; inflammation ; inherited ; mutation ; pneumonia ; population ; prevalence ; protein ; recessive ; sepsis

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

See also Understanding Medical Terminology.

References (6 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: June 2014
Published: February 8, 2016