Based on the knowledge that patients with MCTD have higher levels of anti-U1-RNP antibodies, compared to patients with SLE, it is interesting to note that combined positivity (anti-U1-RNP plus anti-RNP70) results in overall higher anti-U1-RNP antibody levels [12]. This evidence concerns the gene RNPC3 and systemic lupus erythematosus.