RNPC3 and systemic lupus erythematosus: Venn diagrams for autoantibody presence in patients with MCTD and SLE revealed that all of the anti-SMN antibody-positive MCTD patients were also positive for anti-U1-RNP antibody, whereas 95% of anti-SMN antibody-positive SLE patients were also positive for anti-Sm antibody (Fig. 2E).