Plasma nucleic acid analysis by massively parallel sequencing: pathological insights and diagnostic implications

Over the past 15 years there has been increasing interest in the biology and diagnostic applications of circulating DNA in the plasma of human subjects. In particular, DNA from a fetus, a tumour, a transplanted organ and injured tissues has been found in the plasma of pregnant women, cancer patients, transplant recipients and patients suffering from multiple pathologies, respectively. The advent of massively parallel sequencing has given us a quantitative and powerful tool for studying circulating DNA on a genome-wide level. Using this approach, fetal chromosomal aneuploidies can be robustly detected using maternal plasma. Furthermore, a genome-wide genetic map of a fetus can also be constructed using this approach. This method has also allowed one to identify tumour-associated chromosomal translocations, which can then be detected in plasma. The direct application of massively parallel sequencing to the serum of cancer patients has also allowed quantitative aberrations that are associated with malignancy to be detected in serum. The use of massively parallel sequencing on the plasma of transplantation recipients has opened up an approach for detecting rejection. The application of circulating DNA sequencing has also opened up a new method for elucidating the quantitative aberration of circulating DNA in many pathological conditions. Such developments would provide new modalities for molecular diagnostics and would improve our understanding of the biology of circulating nucleic acids.