When compared with stable UCTD, SLE reclassified patients showed significant higher prevalence of joint involvement (81.8% versus 54.6%, p = 0.0001), thrombocytopenia (18.2% versus 6.9%, p = 0.03), positivity for anti-dsDNA (36.4% versus 2.3%, p = 0.0001) and anti-Sm (18.2% versus 1.3%, P = 0.001), low C3 levels (36.4% versus 3.8%, p = 0.001). This evidence concerns the gene C3 and systemic lupus erythematosus.