Besides a higher prevalence and titer of brain-reactive antibodies, NPSLE patients had lower C3 (p <0.001) and C4 (p = 0.043) complement fractions serum levels and higher incidence of anti-P (p = 0.002), anti-NR2 (p = 0.020) and anti-Sm (p = 0.031) antibodies than SLE patients. This evidence concerns the gene C4A and systemic lupus erythematosus.