Preimplantation Genetic Diagnosis (PGD)
Preimplantation Genetic Diagnosis
We are often able to determine if a particular embryo is carrying a specific genetic disease. Through preimplantation genetic diagnosis (PGD), an embryo can be biopsied and the removed cell (or cells) can be analyzed for a specific genetically transmitted disease. This enables patients at risk to greatly reduce the likelihood of having affected children, and in many cases also prevent further transmission of that genetic disorder.
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
- Sickle Cell
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. The biopsied cells are then sent to a specialized lab for genetic analysis. The embryos themselves are typically frozen after biopsy while we await the results of the genetic testing. Those that are normal can be thawed in the next cycle in hopes of achieving a pregnancy. The number of embryos replaced follows standard IVF protocol. These technologies identify which embryos are most likely to produce a normal, unaffected pregnancy.
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 clinical tools.