Preimplantation Genetic Diagnosis (PGD)
What is PGD?
Preimplantation Genetic Diagnosis (PGD) is a method that allows the IVF team to determine which embryos have a normal number of specific chromosomes, or embryos unaffected by a specific disease. These embryos are derived from the In Vitro Fertilization
process. The two techniques for determining the genetic status of an embryo are FISH (fluorescence in situ hybridization) and gene amplification. FISH is used to look for chromosomal abnormalities, and gene amplification is used to determine if an embryo is carrying the gene responsible for certain specific diseases.
What is FISH?
Chromosomal abnormalities in early embryonic cells are analyzed by sophisticated techniques. Fluorescence in situ hybridization (FISH) is used to determine proper structure and the appropriate number of chromosomes 13, 14, 15, 16, 17, 18, 21, 22, as well as the X and Y-chromosomes. Chromosomal translocations, inversions and deletions are some of the many types of disorders diagnosed using PGD with FISH.
Single Gene Defect Analysis
PGD for single gene defect (SGD) uses gene amplification to reveal serious genetic conditions that couples may wish to avoid. Using PGD with SGD, the IVF team
will transfer only embryos diagnosed as unaffected, greatly increasing the chances of having unaffected children.
Partial List of conditions that PGD/FISH and PGD/SGD can detect:
- Cystic Fibrosis
- Duschenne Muscular Dystrophy
- Retinitis Pigmentosa
- Charcot-Marie-Tooth Disease
- Alpha-1-Antitrypsin Deficiency
- Down's Syndrome
- Fragile X Syndrome
- Lesch-Nyhan Syndrome
- Turner Syndrome
- Huntington's Chorea
- Phenylketonuria (PKU)
- Gaucher's Disease
How is PGD Performed?
PGD testing is performed on embryos that result In Vitro Fertilization
. Multiple eggs are retrieved from the ovaries and fertilized with the partner's sperm in our lab. Three days after in vitro fertilization, when each embryo contains 6 to 8 cells, one cell is removed from each embryo through a procedure called Embryo Biopsy. These cells are then sent to a specialized lab for genetic analysis. During the analysis on the single cell, the embryos are kept in culture and allowed to continue to develop. It takes about 48 hours to get the results, and embryos are then transferred at the day-5 blastocyst stage
. These technologies identify which embryos are mostly likely to produce a normal, unaffected pregnancy. The embryos identified as normal or non-affected are then replaced in the uterus. Generally this takes place 6 days after the eggs are retrieved. The number of embryos replaced follows standard IVF protocol. The post procedure treatment follows the same routine as a standard IVF case.
Who should have PGD?
PGD has revolutionized the management of patients at risk for passing on an inherited genetic disease due to a single gene defect. PGD dramatically improves the odds of having a baby without the disorder since affected embryos are identified and not transferred. Some disorders only affect male offspring, so that female embryos may be selected to avoid the condition even if the exact defect isn't understood. Please call our office to learn more about these exciting new clinical tools.