The traditional method for pre-natal screening for Down syndrome entails karyotyping, and the procedure requires two weeks. Researchers from the Howard Hughes Medical Institut, however, have developed a new PCR-based method which can produce accurate results within two hours.
Using a technique known as the digital polymerase chain reaction, Quake and Fan replicated DNA from two cultures of cells growing in the laboratory. One consisted of a normal human cell line and the other had human cells with the Down variant. The digital PCR process allowed the researchers to count DNA molecules from the samples, substituting for the two-week cell culture process traditionally needed to produce enough DNA for karyotyping.
The digital PCR was performed in a commercially available microfluidic chip. The samples were loaded onto the chip, and then partitioned into thousands of chambers by microscopic mechanical valves. While PCR was performed, fluorescent material in the compartments containing individual DNA molecules lit up like an array of LEDs, while those without DNA did not glow. The technique enabled researchers to confirm the presence of abnormal chromosomes typical of Down syndrome with great accuracy.
In addition to speed, the new method are also potentially cheaper, and are semi-automated. The authors also suggest that a simpler non-invasive blood test may even be developed based on the same principles. The study will be published in the Oct. 1, 2007 issue of the journal Analytical Chemistry.