Our test results were all negative, including antithrombin III lupus anticoagulant, antinuclear antibodies, anticardiolipin antibodies, anti-double-stranded DNA antibodies, serum immunoglobulin G production, beta-2 glycoprotein antibodies, lupus anticoagulant, and serum SSB/SSA antibody profile; however, plasma protein C activity decreased (76%, evaluation criteria 82%) while protein S was normal. This evidence concerns the gene PROS1 and systemic lupus erythematosus.