Toward a faster prenatal test for Down syndrome

September 18, 2007

Scientists in California are reporting an advance toward rapid testing for pre-natal detection of Down syndrome and other birth defects that involve an abnormal number of chromosomes.

In a study scheduled for the Oct. 1, 2007 issue of ACS’ journal, Analytical Chemistry, Stanford University bioengineering professor and Howard Hughes Medical Institute researcher Stephen R. Quake and his graduate student H. Christina Fan point out that most existing pre-natal tests depend on a technique termed karyotyping. It requires a two-week wait for anxious parents, while cells taken with amniocentesis or chorionic villus sampling are grown in laboratory culture and analyzed.

Laboratory studies with the new method produced accurate results within two hours. The test is a variation of the famed polymerase chain reaction (PCR) — the basis of the genetic engineering revolution — which produces thousands of identical copies of minute samples of DNA.

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. With the precision derived from counting individual DNA molecules, researchers then were able to move ahead without delay and determine which samples had the extra chromosome that indicates Down syndrome.

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.

Rapid testing alternatives already exist, but they are either too labor-intensive or not applicable to the whole population. “The technique we present in this paper can overcome these limitations. It is rapid and simple. We estimate that the entire procedure from sample collection to result readout would take only a few hours, substantially reducing the anxiety of the expectant parents,” Quake said.

The test is also potentially cheaper than other available methods and semi-automated, reducing the workload of lab personnel. And since the digital PCR technique is based on commercially available lab equipment, any interested physician could use it.

“We are confident that it will work on clinical samples of amniotic fluid or chorionic villus,” Fran said. The next step is to begin clinical trials to evaluate the sensitivity and specificity of the new test. The authors believe the new test could be available in as little as one year.

In addition, Quake cited the possibility that the method could lead to a blood test for Down syndrome. It would involve capturing fetal cells, which leak through the placenta and circulate in the mother’s blood, and analyzing their DNA for abnormalities with digital PCR. Other research groups are also investigating a digital PCR-based Down syndrome test, he noted.

As a non-invasive test, it would be the safest approach to prenatal diagnosis of Down syndrome, since both amniocentesis and chorionic villus sampling pose risks to the fetus. Quake noted, however, that new techniques to separate the small fraction of fetal DNA in a mother’s bloodstream must be developed before a blood test could be developed and tested.

Source: American Chemical Society

Explore further: Researchers find way to ID many pathogens with few DNA probes

Related Stories

Researchers find way to ID many pathogens with few DNA probes

September 29, 2016

Rice University scientists have invented a technology that could potentially identify hundreds of bacterial pathogens simply, quickly and at low cost using a single set of random DNA probes. Rice's "universal microbial diagnostic," ...

Plant disease clinic identifies new case of oak wilt

August 22, 2016

Earlier this year, the Cornell University Plant Disease Diagnostic Clinic (CU-PDDC) used a new rapid test they developed to identify a small number of oak trees with oak wilt disease on Long Island, in the town on Central ...

Frankfurter fraud: Finding out what's in your hot dog

August 10, 2016

Hot dogs are the perfect summer fare. But knowing for sure what you're getting inside a bun can be difficult. Now scientists have devised a method that could help prevent frankfurter fraud, which is especially important for ...

Recommended for you

Shocks in the early universe could be detectable today

October 27, 2016

(—Physicists have discovered a surprising consequence of a widely supported model of the early universe: according to the model, tiny cosmological perturbations produced shocks in the radiation fluid just a fraction ...

Bubble nucleus discovered

October 27, 2016

Research conducted at the National Superconducting Cyclotron Laboratory at Michigan State University has shed new light on the structure of the nucleus, that tiny congregation of protons and neutrons found at the core of ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.