10. Circulating Nucleic Acids as Diagnostic Tool

Circulating nucleic acids are present in small amounts in the plasma of healthy individuals. However the discovery of circulating nucleic acids has long been explored for the noninvasive diagnosis of a variety of clinical conditions. The first studies concerning the detection of circulating DNA were investigated for finding various forms of cancer. Metastasis and recurrence in certain tumour types have been associated with the presence of high levels of cancer-derived DNA in circulation. The detection of fetal DNA in maternal plasma in pregnant women is useful in detecting and monitoring fetal diseases and pregnancyassociated complications. Similarly, levels of circulating DNA in acute medical emergencies including trauma and stroke, have been reported to be increased and have been explored as indicators of clinical severity. In the last few years, other than circulating DNA, much attention and effort has been put into the study of circulating RNA, starting from the detection of tumor-derived RNA in the plasma of cancer patients. Soon after that, detection of circulating fetal RNA in maternal plasma was described. Plasma fetal RNA detection looks to be a promising approach for the development of genderand polymorphism-independent fetal markers for prenatal diagnosis and monitoring complications during pregnancy. This development also opens up the possibility of non-invasive prenatal gene expression profiling by maternal blood analysis.