Anti-DNA antibodies in the primary antiphospholipid syndrome (PAPS)

Primary antiphospholipid syndrome (PAPS) is considered a distinct entity from SLE and patients with PAPS are generally regarded as being dsDNA antibody negative. Levels of IgG and IgM ss and ds DNA antibodies were measured by ELISA in 30 patients who fulfilled the criteria for the diagnosis of PAPS. We compared these patients with 20 normal controls and seven patients with idiopathic SLE. We also examined all the sera for anti-nuclear antibodies by Hep-2 cells and for dsDNA antibodies by Crithidia. We found that 16 patients with PAPS had antibodies to ss and/or dsDNA. Only three of the 16 positive patients had both IgG and IgM anti-DNA antibodies. Twelve patients had anti-nuclear antibodies, but only two were weakly positive for dsDNA antibodies by Crithidia immunofluorescence. Eleven out of 30 patients with PAPS had IgM anti-dsDNA antibodies compared to two out of the seven SLE patients. The PAPS patients with anti-DNA antibodies were clinically indistinguishable from the PAPS patients without antibodies against DNA. Our results show that 53% of patients with PAPS had antibodies to DNA which supports the view that PAPS and SLE are probably overlapping disorders.