New prenatal blood test identifies genetic abnormalities
Non-invasive prenatal tests (NIPTs) are used for foetal genetic disease screening in pregnant women, but established NIPTs have important limitations — including non-informative results. Now, Japanese researchers have developed a non-invasive single-cell DNA assessment method that enables direct extraction of genetic information from live foetal cells for simultaneous evaluation, thereby improving the likelihood of detecting a foetal anomaly.
Using a modified single-cell-based droplet digital PCR (sc-ddPCR) NIPT, the researchers conducted a proof-of-concept study that successfully assessed the genetic information of extremely rare foetal cells in maternal peripheral blood. This modified sc-ddPCR system makes it possible to directly assess single-cell DNA information from live cells without cell-fixation, cell-staining and whole genome amplification steps. The system has been described in The Journal of Molecular Diagnostics.
“Because NIPTs currently analyse small DNA fragments, it can be challenging to ascertain whether the origin of each DNA fragment is the mother or her foetus,” explained lead investigator Dr Kenichiro Hata, Chairman of Maternal-Fetal Biology at Japan’s National Research Institute for Child Health and Development. “We have observed that in some cases NIPT results are discordant with the foetal genetic information that has been reported. This study serves as a proof of concept for non-invasive prenatal diagnosis using circulating foetal cells without any strict cell purification.”
With this modified technique, up to 3000 cells per well can be encapsulated in each droplet and simultaneously analysed. The original sc-ddPCR system simultaneously assesses single-cell genetic information with high sensitivity and specificity. However, the original system is only useful for cell suspensions with a clear background (ie, washed cell lines or clearly sorted cells with fluorescence-activated cell sorting). Researchers modified this sc-ddPCR system to improve the PCR environment in each droplet with higher sensitivity and specificity, which makes it possible to now assess single-cell genetic information from crudely purified nucleated cell samples with impurities.
To confirm the sensitivity of this modified sc-ddPCR system, investigators detected the genomic DNA of circulating male foetal cells in a crudely sorted cell suspension at the single-cell level derived from peripheral blood samples from mothers with male foetuses. Investigators searched for the presence of the sex-determining region Y gene (SRY), which is responsible for the initiation of male sex determination. Analysis of 13 blood samples indicated that only circulating foetal cells from the three pregnant women carrying male foetuses tested positive for the SRY gene, unlike cells from the 10 pregnant women carrying female foetuses. This indicates that the modified sc-ddPCR system not only has high sensitivity, but also high specificity.
“In the future, by optimising cell sorting and encapsulation, as well as generating a more effective PCR environment in each droplet, this modified sc-ddPCR system may be a breakthrough analysis method that can be applied to various research realms and possibly to clinical diagnostic testing,” Dr Hata said.
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