Exciting Developments in the World of Pre-Implantation Genetic Screening
!(http://www.pacificfertilitycenter.com/fertilityflash/vol8-2/dna.jpg "Figure 1. It is now possible to analyze all 23 chromosome pairs from a single embryo.")In the last 2-3 years, as the Human Genome Project has been completed and as more DNA-related biotechnologies have emerged to evaluate human genes, these methods are being utilized to analyze human embryos. The technology now availablethe ability to analyze large numbers of genetic locations on each human chromosome, and quantify that genetic material, with the previously well-established techniques to amplify a single cells genetic material up to hundreds of thousands of copieshas allowed PGS to take a quantum leap forward. It is now possible to more accurately analyze all 23 chromosome pairs from a single embryo; not only to determine if the correct number of copies of each chromosome is present, but also to look at single gene mutations. At the end of 2009, Pacific Fertility Center began working with a new biotech company called Gene Security Network, located in Redwood City ([genesecurity.net](http://www.genesecurity.net/)). This company uses gene microarray technology to analyze amplified DNA from a single cell. It then uses microchips to analyze 30,000 genetic loci in a quantitative manner. In addition, their unique technology allows us to compare the analysis of the embryos cells to the parents chromosomes to ensure that all the genes are being properly analyzed. It does appear that the error problems that plagued FISH technology have been overcome with this new, more sophisticated, method. In October of 2009, Dr. Conaghan and I were invited to tour the GSN laboratory and see the technology in action. We met with David Johnson, the lead scientist at GSN, who explained the cell process; from the amplification of the DNA, to arranging the chromosomes on chips, to DNA analysis, to synthesizing the data generated with the parental genetic data to come up with a full analysis of that cells genome. In order to process the cells between the day of embryo biopsy (Day 3) and receive the results on the day of embryo transfer (Day 5), their technicians work around the clock in shifts. GSN has a very cold, clean room to replicate the single cells into multiple copies. They cannot allow any outside contamination, not even from a single cell. They videotape the cell duplicating process so if any errors subsequently arise, they have a video record of what the laboratory technician did. We found this to be very impressive. We also saw how the chips were coated with DNA and analyzed. We were shown the sophisticated software that generates the final report detailing the genetic makeup of each embryo from the cells in which they originated. All in all, the tour gave us great confidence in the quality control and scientific integrity at GSN. Even with this 21st century technology, we continue to biopsy Day 3 embryos because it provides us with a 48 hours window to send the cells to the lab and complete the analysis in time for transfer. However, we have not yet found a way around the problem of mosa- icism. GSN and microarray technology appears to have largely solved the resolution error problem but it can only tell us what is in the chromosomal make-up of the single cell. It cannot tell us whether or not that cell represents what is truly going on with the rest of the embryo. We are currently looking at the possibility of biopsying Day 5 embryos. The set back would result in having to freeze these embryos due to the time constraint in analyzing the genetic material in time for fresh transfer. With all of the innovation occurring daily in the genetics field, we hope that this puzzle will be resolved. Carolyn Givens, M.D.
First and foremost is the error rate in determining whether there are 0, 1, 2 or more signals from any one chromosomea problem which is compounded by the more chromosomes one wishes to count from that single cell. The error rates in some studies have been reported to be as high as 50%, making PGS by FISH essentially no better than guesswork. The second issue is mosaicism. This refers to the fact that not all cells in a Day 3 embryo are identical. Some cells may be abnormal whereas the rest are normal. The normal cells can grow preferentially and create a normal embryo by implantation. However, if the cell biopsied was abnormal, that embryo would not be transferred because of obvious concern that it may result in an abnormal early pregnancy. PGS using FISH has failed to show any benefit in improving implantation and pregnancy rates in IVF. All of these factors have seriously limited the patient population for whom we have recommended this diagnostic testing.
Previous Fertility Flash articles about PGS: [2 Methods of Gaining Info Prior to Implantation ](http://www.pacificfertilitycenter.com/fertilityflash/vol2_issue4.php#content7) [PGD & PGS: Why Genetic Counseling is a Prerequisite](http://www.pacificfertilitycenter.com/fertilityflash/vol2_issue4.php#content3) [The Benefits and Pitfalls of PGS](http://www.pacificfertilitycenter.com/fertilityflash/vol2_issue9.htm#article1)