The mean C4A and C4B concentrations were 10.0 (9.2–10.8) mg/dL and 8.7 (8.1–9.4) mg/dL, respectively, in the SLE group; and were 11.6 (10.9–12.4) mg/dL and 10.1 (9.4–10.8) mg/dL, respectively, in the non-SLE group (p = 0.0038 for C4A; p = 0.005 for C4B). The gene discussed is C4A; the disease is systemic lupus erythematosus.