https://doi.org/10.1351/goldbook.13030
Congenital deficiency in any of the various components of the complement system.
Note: Rheumatic disorders [mainly systemic lupus erythematosus (SLE)] are associated with deficiencies of the early components of the classical pathway. More than \(\pu{30\%}\) of individuals with C2 deficiency and nearly \(\pu{80\%}\) with either C3 or C4 deficiency have an autoimmune manifestation.