Complement deficiency

Complement pathway

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Complement deficiency is a condition characterized by the absence or dysfunction of one or more components of the complement system, which is a crucial part of the immune system. The complement system consists of a series of small proteins that work together to fight infections, clear damaged cells, and promote inflammation.

Types of Complement Deficiency

Complement deficiencies can be classified based on which component of the complement system is affected. The main types include:

• C1q, C1r, C1s, C4, and C2 deficiencies: These deficiencies affect the classical pathway of complement activation.
• C3 deficiency: This affects the central component of the complement system and can lead to severe infections.
• C5, C6, C7, C8, and C9 deficiencies: These affect the membrane attack complex (MAC) and can lead to increased susceptibility to Neisseria infections.
• Factor D, Factor B, and Properdin deficiencies: These affect the alternative pathway of complement activation.
• Mannose-binding lectin (MBL) deficiency: This affects the lectin pathway of complement activation.

Causes

Complement deficiencies can be inherited or acquired. Inherited deficiencies are usually due to genetic mutations that affect the production or function of complement proteins. Acquired deficiencies can result from conditions such as autoimmune diseases, liver disease, or certain infections.

Symptoms

The symptoms of complement deficiency vary depending on the specific component that is deficient. Common symptoms include:

• Recurrent bacterial infections, particularly with encapsulated bacteria like Streptococcus pneumoniae and Neisseria meningitidis.
• Increased susceptibility to autoimmune diseases such as systemic lupus erythematosus (SLE).
• Chronic inflammation and tissue damage.

Diagnosis

Diagnosis of complement deficiency typically involves:

• Blood tests to measure the levels and activity of complement proteins.
• Genetic testing to identify mutations in complement-related genes.
• Functional assays to assess the activity of the complement pathways.

Treatment

Treatment for complement deficiency depends on the specific type and severity of the condition. Options may include:

• Antibiotic prophylaxis to prevent infections.
• Immunizations to protect against specific pathogens.
• Plasma infusions or complement replacement therapy in certain cases.

Prognosis

The prognosis for individuals with complement deficiency varies. With appropriate management, many individuals can lead relatively normal lives. However, the risk of severe infections and autoimmune complications remains a concern.

See Also

• Immune system
• Autoimmune disease
• Genetic disorder
• Infection