Partial C4A deficiency is associated with susceptibility to systemic lupus erythematosus in black Americans.

In a study of 59 black American patients with systemic lupus erythematosus (SLE), we found that partial C4A deficiency occurred twice as frequently as in 59 control subjects (32.3% versus 15.3%; P = 0.02). Complete C4A deficiency, however, occurred in only 1 patient and in no controls. Partial C4A deficiency is a risk factor for SLE in black, as well as in white, SLE populations studied to date. In contrast with white patients, complete C4A deficiency occurs relatively infrequently in black patients with SLE.