Complement 3 deficiency

Protein C3 PDB 1c3d

Complement 3 deficiency is a rare immunodeficiency disorder characterized by the body's inability to produce a sufficient amount of Complement component 3 (C3), a crucial protein in the immune system. C3 plays a vital role in the activation of the complement system, a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism. This deficiency can lead to an increased susceptibility to bacterial infections, particularly infections caused by encapsulated bacteria, and can also contribute to the development of autoimmune conditions.

Causes

Complement 3 deficiency is most often caused by a genetic mutation that affects the production or function of the C3 protein. These mutations are typically inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the mutated gene, one from each parent, to be affected by the condition.

Symptoms

The symptoms of Complement 3 deficiency can vary widely among individuals but commonly include an increased susceptibility to infections, particularly those caused by encapsulated bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis. These infections can be recurrent and severe. Additionally, individuals with Complement 3 deficiency may experience autoimmune problems, such as systemic lupus erythematosus (SLE) or glomerulonephritis, due to the immune system attacking the body's own tissues.

Diagnosis

Diagnosis of Complement 3 deficiency typically involves blood tests to measure the levels of complement proteins in the blood. Low levels of C3, in the presence of normal levels of other complement components, may suggest a diagnosis of Complement 3 deficiency. Further genetic testing may be conducted to identify specific mutations in the genes responsible for C3 production.

Treatment

There is no cure for Complement 3 deficiency, and treatment focuses on managing symptoms and preventing infections. This may include the use of antibiotics to treat and prevent bacterial infections and immunosuppressive drugs to manage autoimmune symptoms. In some cases, vaccination against encapsulated bacteria may be recommended to reduce the risk of infection.

Prognosis

The prognosis for individuals with Complement 3 deficiency varies depending on the severity of the condition and the presence of associated autoimmune disorders. With appropriate treatment and management of infections, individuals can lead relatively normal lives. However, they may require ongoing medical care to manage the increased risk of infections and autoimmune complications.