Terminal Complement Deficiencies (C5–C9)

Terminal Complement Deficiencies (C5–C9) are rare immune system disorders where the body lacks certain proteins that help fight infections. These proteins are part of the complement system, which is crucial for defending against bacteria, especially a type called Neisseria. When these proteins are missing or not working, people are more likely to get serious infections like meningitis or bloodstream infections. The condition mainly affects the immune system and its ability to kill bacteria. Symptoms often include repeated infections that can be severe and life-threatening. Early recognition is important because these infections require prompt medical attention. This condition highlights the importance of the complement system in protecting the body from certain dangerous bacteria.

Terminal Complement Deficiencies (C5–C9) refer to inherited or acquired defects in the terminal components of the complement cascade, specifically proteins C5 through C9. These proteins form the membrane attack complex (MAC), which creates pores in the membranes of target pathogens, leading to their lysis. Deficiency in any of these components impairs MAC formation, resulting in defective bacterial killing, particularly of Neisseria species. The condition is usually caused by genetic mutations in the genes encoding these complement proteins or rarely by autoantibodies. Clinically, it manifests as increased susceptibility to recurrent, invasive Neisserial infections such as meningococcemia and meningitis. Diagnosis is significant because it identifies patients at risk for life-threatening infections and guides preventive strategies. The deficiency does not typically increase susceptibility to other types of infections, highlighting the specificity of the terminal complement pathway in defense against Neisseria.