May 21, 2024

Preimplantation Genetic Diagnosis: Understanding the Process

Pharmaceuticals

Preimplantation genetic diagnosis, commonly known as PGD, is an assisted reproductive technique used mainly for couples at high risk of transmitting genetic diseases to their offspring. PGD screens embryos prior to implantation in the womb for genetic abnormalities such as chromosomal disorders like Down syndrome, as well as single-gene disorders like cystic fibrosis. By identifying genetic diseases prior to pregnancy, PGD allows parents to choose healthy embryos for implantation, thereby preventing the transmission of genetic diseases. In this article, we explore the various aspects of PGD in more depth.

What is PGD?

Preimplantation genetic diagnosis refers to the genetic testing of embryos created through in-vitro fertilization, before pregnancy. During the IVF process, multiple eggs are retrieved from the mother and fertilized with sperm in a lab to create embryos. Typically 3-5 days after fertilization, when the embryos have developed to the 6-10 cell stage, one cell is removed from each embryo without damaging embryo development. The removed cells are then tested for genetic abnormalities and chromosome defects through techniques such as fluorescence in situ hybridization and next-generation DNA sequencing. Only healthy, genetically normal embryos are selected for implantation in the mother’s uterus with the goal of establishing a successful pregnancy.

Benefits of PGD

There are several advantages that PGD offers to at-risk couples. Firstly, it prevents the transmission of inherited genetic disorders to offspring. Couples that undergo PGD have healthy, disease-free babies. This is especially important for diseases with no cure. PGD also allows parents to have unaffected children of their own rather than needing to consider alternatives like adoption. It reduces the psychological and financial burden of multiple miscarriages, terminations and caring for a child with genetic disabilities. PGD saves parents and families from the emotional trauma of learning late in pregnancy that the fetus is affected.

Application of PGD

PGD is used most commonly for severe monogenic or single gene disorders with a high risk of being passed to children such as cystic fibrosis, muscular dystrophy, hemophilia, and Tay-Sachs disease. It is also effective for diagnosing chromosomal abnormalities like Down syndrome, Turner syndrome, Klinefelter syndrome, and transferable translocations. PGD has expanded over the years to detect many familial cancer gene mutations as well. Couples with a family history of hereditary cancers like breast and ovarian cancer, hereditary non-polyposis colon cancer can screen embryos for mutations in genes such as BRCA1, BRCA2 and MLH1 using PGD.

PGD Procedure

At present, the standard PGD procedure takes approximately 4-6 weeks to complete and involves the following steps:

1. Controlled ovarian hyperstimulation of the prospective mother with fertility drugs to develop multiple mature eggs.

2. Egg retrieval via ultrasound-guided needle aspiration of the ovaries.

3. Insemination of eggs with sperm to create pre-embryos through conventional IVF or intracytoplasmic sperm injection (ICSI).

4. Pre-embryo culture for 3-5 days until the 6-10 cell stage.

5. Removal of a single cell from each pre-embryo by micromanipulation without damaging embryo development.

6. Analysis of the removed cell for genetic/chromosomal abnormalities through techniques like PCR, FISH or NGS.

7. Selection of unaffected embryos for uterine transfer and cryopreservation of remaining normal pre-embryos.

8. Implantation of 1 or 2 healthy embryos into the uterus with the goal of establishing a successful pregnancy.

Limitations and Ethical Considerations

While PGD offers benefits, it also raises some ethical and safety concerns. There is a risk of misdiagnosis during testing. Mosaic embryos where not all cells have the same genotype cannot be reliably diagnosed. PGD requires IVF and there are risks involved with ovarian stimulation and multiple pregnancies from embryo transfer. It could potentially lead to the selection of embryos based on non-medical traits like gender or tissue matching, raising eugenics issues. There are also arguments that it contributes to the “commodification” of embryos. Overall, most experts agree that PGD is acceptable when used to avoid serious genetic diseases and disability in future children. With appropriate oversight and regulation, it can enable parents to have healthy biological offspring.

Conclusion

In summary, preimplantation genetic diagnosis provides an effective way for at-risk couples to have children free of inherited genetic diseases. By screening embryos prior to implantation, it prevents transmission of disorders to offspring. While it raises some ethical issues, most experts agree that PGD is an important medical advancement when used for severe genetic conditions with strong family histories. With further refinement of testing techniques and addressing of limitations, PGD will likely become more widely used in the future to selectively transfer healthy embryos. This will fulfill the reproductive choices of many parents seeking to have children unaffected by disabilities or terminal illnesses.

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  1. Source: Coherent Market Insights, Public sources, Desk research
  2. We have leveraged AI tools to mine information and compile it