THE PHENOTYPE OF SLE ASSOCIATED WITH COMPLETE DEFICIENCY OF COMPLEMENT ISOTYPE C4A

Complete deficiency of the complement C4A isotype is a known genetic r isk factor for systemic lupus erythematosus (SLE). The disease phenoty pe of C4A-deficient patients has never been defined. Among 200 patient s with SLE from five centers, 18 (9%) with C4A deficiency were identif ied. These individuals were compared to those who were C4A replete wit h regard to a series of clinical and serologic features. The only sign ificant differences between the two groups were in the presence of ren al disease (C4A deficient, 11%; C4A replete, 46%; P < 0.006) and a dec rease in the serum concentrations of C3 (C4A deficient, 11%; C4A reple te, 35%; P < 0.04). There was also a trend for the C4A-deficient indiv iduals to have milder disease. In light of the tendency for C4A-defici ent individuals to have lower serum concentrations of C4, it is import ant that such patients not be subjected to overly aggressive efforts t o ''normalize'' their C4 levels.