Dosage and characterization of circulating DNA: present usage and possible applications in systemic autoimmune disorders

The discovery of extracellular nucleic acids in the circulation was firstly reported in 1948. In the last few years it has been demonstrated that the entire spectrum of genetic changes seen in primary tumors could also be detected in the serum of patients with solid tumors. This observation has also opened up exciting possibilities for tumor detection and monitoring. More recently investigators started looking for other forms of non-host DNA in the plasma/serum so that in 1997 the presence of fetal DNA in the plasma/serum of pregnant women was demonstrated. This finding suggested that maternal plasma fetal DNA would be a very valuable material for noninvasive prenatal diagnosis and monitoring. It has been also postulated that the presence of the two-way trafficking of nucleated cells and free DNA between the mother and fetus may have potential implications for the development of certain autoimmune diseases. Concerning autoimmune disorders, Tan was the first author to describe the presence of high levels of circulating DNA in patients with systemic lupus erythematosus (SLE) in 1986. Later on different authors demonstrated that elevated levels of serum DNA was also present in patients with other diseases including rheumatoid arthritis. We have analyzed both circulating free DNA and DNA extracted from nucleated blood cells in scleroderma and in lupus patients but, by using gel electrophoresis, we were able to define the pattern of the DNA, instead of simply dosing its amount in the circulation. We have found that SLE and SSc have anomalous patterns of DNA both in serum and in the Buffy-coat and that these patterns are typical for each disorder. It is possible that understanding the biological significance of the diversity in DNA pattern exhibition in white blood cells may give new insights into the pathophysiology of autoimmune disorders. It is also conceivable that circulating and immune-competent cellular DNA markers might offer the promise of precise quantitative analysis useful for diagnostic purposes, without the need to establish difficult cutoffs as is necessary for protein markers.