Frontiers in Preimplantation Genetic Diagnosis and Screening (PGD/S)

By: Gary L. Harton, BS, TS(ABB) and Shelby Duffer, MS, CGC

Preimplantation genetic diagnosis (PGD) was first developed in 1990. Dr. Alan Handyside's lab in London was the first to be able to take a single cell from a three-day old embryo and use the genetic material inside that cell to run a genetic test. This allowed him to choose embryos that would not have the specific genetic disease carried by the biological parents. Since the embryos were screened before implantation, there were fewer worries about the health of an ongoing pregnancy and increased chances that any required prenatal testing would be normal. PGD was a revolution in genetic testing and was quickly adopted by a number of assisted reproductive technology (ART) centers around the world. Today, PGD is available for a large variety of genetic diseases. In recent years, it has been proposed that preimplantation information about embryos might be helpful for many couples experiencing infertility. Abnormalities in the chromosomes (the genetic material inside the cell) are responsible for a large percentage of pregnancy losses. Preimplantation genetic screening (PGS) is the testing of a single cell from an embryo for these common chromosomal anomalies. Our expectation is that finding and eliminating chromosomally abnormal embryos during an IVF cycle will increase pregnancy rates and help patients deliver more healthy children. Currently PGD only examines a few of the 24 human chromosomes. This detects common abnormalities, but leaves many untested. New technologies are emerging that will allow testing of all 24 chromosomes for errors as well as the ability to combine general chromosome screening with specific genetic disease diagnosis. Genetics & IVF Institute (GIVF) is collaborating with the father of PGD, Dr. Alan Handyside (The London Bridge Fertility, Gynecology and Genetics Centre, London) on a new PGD technology called Karyomapping. Our collaboration presented data this year describing this technique at the prestigious American Society for Reproductive Medicine (ASRM) meeting. It allows the simultaneous detection of anomalies in all 24 chromosomes and virtually any genetic disease in embryos. The ASRM meeting also included presentations on another new PGD technique called comparative genomic hybridization (CGH). An American/English partnership showed initial information confirming very good pregnancy rates into the third trimester following testing of all 24 chromosomes. GIVF continues to be a leader in the development of new technologies and new applications of science to assisted reproduction and infertility treatment. These new techniques may be the next step in allowing doctors and scientists to choose the best embryos for transfer in IVF cycles.