Complete C4B deficiency in black Americans with systemic lupus erythematosus.

We report 3 black American patients with systemic lupus erythematosus (SLE) in whom C4B was completely deficient in plasma. They all exhibited antibody against the nucleoprotein antigen SSA (Ro), as well as cutaneous involvement, features that have been previously associated with complement deficiency states. IgG antibody against cardiolipin was also present in 2 patients, in association with a biologic false positive test for syphilis in one patient, and with thrombocytopenia in another. This is the first description of the clinical presentation of complete C4B deficiency in blacks with SLE.