At group level, the mean titres of anti-PTX3 antibodies were significantly higher in seronegative compared with seropositive RA patients (P = 0.0322; Fig. 3), and values above the cut-off for SLE (>0.234 nm) were significantly more prevalent in seronegative (8/41) than seropositive (0/42) RA patients (19.5% vs. 0%, P = 0.002). This evidence concerns the gene PTX3 and rheumatoid arthritis.