Levels of plasma cell-free DNA and its correlation with disease activity in rheumatoid arthritis and systemic lupus erythematosus patients

BackgroundCell free deoxyribonucleic acid (cf-DNA) is now emerging as a useful tool for non-invasive diagnostic methods related to a wide range of clinical conditions including autoimmune diseases.Aim of the workTo estimate the concentration of plasma cf-DNA in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients compared with healthy subjects and to correlate the results with clinical and laboratory parameters of disease activity.Patients and methodsThe study included 30 RA patients, 35 SLE patients and 25 matched control. Plasma cf-DNA was estimated by real-time quantitative PCR. Disease activity parameters for each disease were assessed; Disease Activity Score-28 (DAS28) was used for RA and SLE disease activity index 2000 (SLEDAI-2K) for SLE patients.ResultsThe RA patients (F:M 4:1) had a mean age of 36.8 ± 9.6 years and disease duration of 8.3 ± 1.1 years while the SLE patients (F:M 7.75:1) had a mean age of 35.6 ± 8.8 years and disease duration of 8.1 ± 0.87 years. There was a highly significant increase in the cf-DNA level in SLE patients (17.33 ± 2.4 ng/ml) and RA patients (11.15 ± 2.3 ng/ml) compared to the level in the control (4.15 ± 1.4 ng/ml) (p = 0.0005). The cf-DNA significantly correlated with the erythrocyte sedimentation rate (ESR) (p = 0.04), C-reactive protein (p = 0.04) and the DAS28 (p = 0.005) in the RA patients and with the ESR (p = 0.03), anti-ds-DNA (p = 0.008), complement-4 (p = 0.04) and SLEDAI-2K (p = 0.002).ConclusionThe increased cf-DNA implicates a possible role in the pathogenesis of both RA and SLE and appears to be a useful marker of disease activity in addition to other laboratory tests.