Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Genetic testing still smart choice, despite uncertainties

21.12.2005


Technique to pick healthy embryos highly reliable, but small margin of error remains



Screening embryos for genetic diseases during in vitro fertilization offers couples the best chance for a healthy child, but a genetic glitch could potentially cause doctors to misdiagnose a small fraction of them, University of Florida researchers say.

Citing concerns about the accuracy of preimplantation genetic diagnosis, the method many practitioners use to pick the healthiest embryos during IVF, UF researchers set out to study the procedure. Their work, described during a recent meeting of the American Society of Reproductive Medicine, reveals the technique is actually highly reliable. But because there is a slim chance a genetic abnormality can cause doctors to misdiagnose embryos, some concerns still need to be addressed, the researchers said.


Preimplantation genetic diagnosis has been used for more than a decade to screen embryos for hereditary diseases such as Down syndrome and other abnormalities. To do this, one cell from an eight-cell embryo is extracted and examined for chromosomal defects.

However, as many as half these embryos spawn cells with different genetic information as they divide, giving doctors an inaccurate idea of how the embryo will continue to develop, said Larissa Kovalinskaia, M.S., a UF research associate with the College of Medicine’s IVF program. While many embryos with this abnormality - called chromosomal mosaicism - stop developing early, some go on to be born. Because these embryos’ cells contain different sets of chromosomes, doctors cannot always accurately screen them for genetic diseases, Kovalinskaia said.

"As more data were coming out, saying that as many as 50 percent of (IVF) embryos were mosaic, we started worrying about the accuracy of preimplantation genetic diagnosis," she said. "When you take one cell, does it represent the entire embryo? What we’ve shown is that we can rely on PGD."

UF researchers estimate less than 3 percent of healthy embryos are discarded as abnormal and only 1.5 percent are implanted with undetected genetic defects because of mosaicism.

To find out how big of a problem mosaicism is, the researchers developed a mathematical model using data from UF’s IVF program and other programs to illustrate the different paths an embryo takes as it develops. While half of embryos turn out normal, with no mosaicism, the other half produce irregular cells as they divide.

Embryos that become mosaic after their cells divide twice typically stop progressing by the time they have accumulated eight cells. Too many of their cells have chromosomes that don’t match and these mixed messages lead the embryo to stop developing, Kovalinskaia said.

Embryos with only one or two irregular cells still have a chance to develop normally though, she said. These embryos tend to not develop this abnormality until after their cells have divided a third time, typically the time when doctors perform preimplantation genetic diagnosis. This is where the problem with diagnosis occurs, researchers say.

"Our pathway concept may help to explain the observed outcomes during preimplantation diagnosis," said Kenneth Drury, Ph.D., director of the UF IVF and Andrology Laboratory and a clinical professor in the College of Medicine who was one of the researchers. "When we biopsy an eight-cell embryo, if we choose (the one) normal cell in an abnormal embryo, we may think that embryo is normal and transfer it.

"This occurs about 1 percent of the time, which means 99 percent of the time we will be accurate. Again the error is not due to a technical mistake but to natural errors occurring during early cell division in the embryo."

Extracting test cells before the embryo divides a third time could reduce the number of misdiagnoses because of mosaicism, the UF researchers suggest. Improving culture conditions could help too, Kovalinskaia said.

But the small margin of error shouldn’t stop couples from having preimplantation genetic diagnosis, said Jamie Grifo, M.D., Ph.D., a professor of obstetrics and gynecology at New York University. The testing can work miracles for women prone to miscarriages or who carry genetic diseases, he said.

"If you are at risk for genetic diseases, it changes your outlook on starting a family," he said. "PGD allows them to get pregnant. It’s a dramatic improvement when it works."

More than 45,000 babies are born each year with the aid of assisted reproductive technologies like IVF, according to the Centers for Disease Control and Prevention. The use of IVF has declined in recent years, but Grifo said that is largely because baby boomers are leaving their childbearing years. Technologies like preimplantation genetic diagnosis have helped too, making IVF more accurate, he said.

"There has been a lot of progress," Grifo said. "It’s helped many patients."

April Frawley Birdwell | EurekAlert!
Further information:
http://www.vpha.health.ufl.edu

More articles from Life Sciences:

nachricht Topologische Quantenchemie
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

nachricht Topological Quantum Chemistry
21.07.2017 | Max-Planck-Institut für Chemische Physik fester Stoffe

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>