Molecular heterogeneity of c2 deficiency

The most common of the complement deficiencies in populations of European origin is a genetic deficiency of the second component of complement (C2).¹ Rheumatologic disorders such as systemic lupus erythematosus, Henoch—Schönlein purpura, and polymyositis have been recognized in more than half the patients with this deficiency. To a lesser extent, C2 deficiency has been associated with increased susceptibility to infection.² Genes encoding the proteins C2 and C4 (the fourth component of complement) of the classic complement-activation pathway and factor B of the alternative pathway are located in the major histocompatibility complex (MHC) on the short arm of chromosome 6 between.