Complement component 8 deficiency

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Reviewed December 2015

What is complement component 8 deficiency?

Complement component 8 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. People with complement component 8 deficiency have a significantly increased risk of recurrent bacterial infections, particularly by a bacterium called Neisseria meningitidis. Infection by this bacterium causes inflammation of the membranes surrounding the brain and spinal cord (meningitis). Although meningitis can be life-threatening, individuals with complement component 8 deficiency are less likely to die from the infection than people in the general population who contract it.

The severity of complement component 8 deficiency varies widely. While some people with this condition experience one or more infections, others do not have any health problems related to the disorder.

There are two types of complement component 8 deficiency, types I and II, classified by their genetic cause. The two types have the same signs and symptoms.

How common is complement component 8 deficiency?

Complement component 8 deficiency is a rare disorder, although its prevalence is unknown. Type I occurs in several populations, particularly in people with Hispanic, Japanese, or African Caribbean heritage, whereas type II primarily occurs in people of Northern European descent.

What genes are related to complement component 8 deficiency?

Complement component 8 deficiency is caused by mutations in the C8A or C8B gene. C8A gene mutations underlie type I, and C8B gene mutations cause type II. These genes provide instructions for making pieces of a protein complex called complement component 8. This complex is composed of an alpha subunit, produced from the C8A gene, a beta subunit, produced from the C8B gene, and a gamma subunit, produced from another gene called C8G.

Complement component 8 aids in 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. Complement component 8 combines with several other complement proteins to form the membrane attack complex (MAC), which inserts itself in the outer membrane of bacterial cells. This complex creates a hole (pore) in the membrane, which kills the bacterium.

Mutations in either C8A or C8B lead to a shortage of the respective subunit, which impairs formation of complement component 8. Without complement component 8, membrane attack complexes cannot form, which impairs the immune response, particularly against Neisseria meningitidis. This impaired immune response leaves affected individuals prone to recurrent episodes of meningitis.

How do people inherit complement component 8 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 8 deficiency?

These resources address the diagnosis or management of complement component 8 deficiency and may include treatment providers.

You might also find information on the diagnosis or management of complement component 8 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 8 deficiency?

You may find the following resources about complement component 8 deficiency helpful. These materials are written for the general public.

MedlinePlus - Health information (4 links)
Additional NIH Resources - National Institutes of Health
National Institute of Allergy and Infectious Diseases: Primary Immune Deficiency Diseases
Educational resources - Information pages (9 links)
Patient support - For patients and families (3 links)

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

Genetic Testing Registry - Repository of genetic test information (2 links)
ClinicalTrials.gov - Linking patients to medical research
PubMed - Recent literature
OMIM - Genetic disorder catalog (2 links)

What other names do people use for complement component 8 deficiency?

C8 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 8 deficiency?

Ask the Genetic and Rare Diseases Information Center

Where can I find general information about genetic conditions?

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 complement component 8 deficiency?

autosomal ; autosomal recessive ; bacteria ; cell ; complement proteins ; deficiency ; gene ;immune response ; immune system ; immunodeficiency ; infection ; inflammation ; inherited ;population ; prevalence ; protein ; recessive ; subunit

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

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