Early Complement Deficiencies (C1–C4)

Early Complement Deficiencies (C1–C4) are rare conditions affecting the body's immune system, specifically the complement pathway, which helps fight infections and clear damaged cells. These deficiencies involve problems with the first four proteins in the complement cascade, leading to a weakened ability to defend against certain bacteria and to remove immune complexes. People with these deficiencies often experience recurrent infections, especially with bacteria like Neisseria species, and may develop autoimmune diseases such as systemic lupus erythematosus. The condition primarily impacts the blood and immune system, increasing vulnerability to infections and immune system malfunctions. Early diagnosis is important to manage symptoms and prevent complications.

Early Complement Deficiencies (C1–C4) refer to inherited or acquired defects in the classical complement pathway components C1q, C1r, C1s, C2, C3, and C4. These deficiencies impair the classical pathway activation, leading to defective opsonization, immune complex clearance, and increased susceptibility to infections and autoimmune diseases. The most common clinical manifestations include recurrent bacterial infections, particularly with encapsulated organisms like Neisseria meningitidis, and a high risk of autoimmune disorders such as systemic lupus erythematosus due to impaired clearance of apoptotic cells and immune complexes. The underlying cause is often genetic mutations affecting complement protein synthesis or function. Early complement deficiencies are distinguished from late complement deficiencies by their involvement in the initial steps of the classical pathway and their association with autoimmune phenomena.