C4A and systemic lupus erythematosus: C4A and C4B showed high CNV in the present study, and one copy of C4B (OR = 1.6051, P = 0.0331) was significantly associated with SLE, which is partially consistent with a previous report that suggested that one copy of C4A (OR = 1.613, P = 0.022) was a risk factor for SLE susceptibility7.