What is PGD?
Preimplantation genetic diagnosis (PGD) refers to a technique used for genetic screening of embryos prior to implantation and pregnancy. During in vitro fertilization (IVF), one or two cells are biopsied from embryos 3-5 days after fertilization, while they are still composed of only 8 cells. The biopsied cells are then analyzed for genetic defects or chromosomal abnormalities. Only healthy, unaffected embryos are selected for transfer back into the mother’s uterus in hopes of establishing a successful pregnancy.
PGD allows for the identification of genetic conditions. Couples who have a known risk of passing on genetic disorders may undergo Preimplantation Genetic Diagnosis to select embryos that do not have the abnormal gene(s) in question. Common reasons people utilize PGD include screening for cystic fibrosis, sickle cell anemia, Tay-Sachs disease, chromosome rearrangements like translocations, and other single gene disorders. PGD is also sometimes used for medical reasons like checking for HLA tissue compatibility between an existing child and new embryo.
The Process of PGD
The exact steps of PGD are as follows:
1. The woman undergoes ovarian stimulation and egg retrieval as part of a standard IVF cycle. Eggs are fertilized with sperm in the laboratory to create embryos.
2. Around day 3 after fertilization when the embryos have developed to the 8-cell stage, one or two cells are removed from each embryo through a biopsy procedure performed under a microscope.
3. The biopsied cells are analyzed for the known genetic defect/abnormality using techniques like PCR, FISH, or NGS. Testing is tailored to the specific indication.
4. Only unaffected embryos that are free of the mutation, chromosome abnormality, or condition in question are selected for implantation back into the mother’s uterus. Typically 1-2 embryos are transferred.
5. The remaining unaffected, biopsied and tested embryos may be frozen for later use in frozen embryo transfers if the first attempt is unsuccessful.
Potential Benefits and Drawbacks of PGD
While PGD can enable couples to avoid passing on serious genetic disorders to their children, the technique is not without controversy. Some argue it promotes eugenics by allowing selection of embryos based on detected traits. There are also limitations to the information that can be determined from a small biopsy sample, so PGD is not a guarantee against unforeseen health issues. Furthermore, the process of IVF and embryo biopsy carries risks of multiple pregnancy, miscarriage, or failure to form a healthy pregnancy. However, proponents emphasize the benefits of avoiding the suffering of genetic diseases for families as well as the potential children. PGD alleviates guilt, uncertainty, and feelings of grief after painful terminations or losses of affected pregnancies. Overall, it is a complex procedure that requires considerable counseling and decision making for families.
Ethical Considerations Surrounding PGD
Perhaps the most debated aspect of PGD revolves around its ethical implications. There are three primary areas of ethical concern:
1. Eugenics: Some argue PGD could promote the selection of embryos based on non-medical traits like gender or physical characteristics, crossing into the realm of “designer babies” and eugenics. However, most clinics only conduct testing for diagnosed genetic defects or serious conditions.
2. Discrimination against disabilities: Critics contend PGD reflects societal biases against people with disabilities by deeming their lives not worth living. Defenders counter that parents have a right to avoid transmitting conditions that cause suffering.
3. Commodification of embryos: The process of IVF and embryo biopsy raises issues about the moral status of embryos and whether they should be created or destroyed in the name of genetic selection. Regulating the number of embryos created and their use attempts to address this concern.
Overall, balancing individual reproductive autonomy with societal implications poses complex challenges regarding PGD. While it enables prevention of disease, widespread use could impact ideas about genetic equality and human diversity. Open discussion continues regarding appropriate limitations and uses.
Future Directions for PGD
As genetic testing capabilities advance, PGD technologies are evolving as well. Recent progress includes:
– Expanded applications: Beyond single-gene disorders, PGD is applicable to conditions with complex inheritance patterns and aneuploidy screening for all 24 chromosomes. It holds promise for detecting later-onset diseases with a genetic component like some cancers.
– Improved diagnosis: Transition from FISH to microarrays and next-generation sequencing allows analysis of larger DNA regions and multiple conditions simultaneously from a single biopsy. This boosts accuracy.
– Tissue biopsies: Taking a trophectoderm biopsy from the outer layer may prove safer than traditional inner cell biopsies as embryos develop further.
– Embryo-wide analysis: Whole genome sequencing of individual blastomeres before embryo transfer could eventually provide more comprehensive data than testing from a single cell.
As technology improves our understanding of genetics, PGD will likely continue expanding our reproductive options. But it also highlights societal responsibilities to ensure ethical, equitable access to these powerful techniques. Balanced regulation and open discussion remains important to maximize benefits and minimize unintended consequences.
In summary, PGD is a complex technique that enables couples to screen embryos for genetic diseases and conditions prior to implantation. While it helps many families avoid transmission of serious disorders, PGD also involves debates around eugenics, discrimination, and commodification of embryos. Both benefits and drawbacks exist. As testing methods evolve to provide more comprehensive diagnoses from fewer cells, PGD holds promise but also responsibility. Moving forward, balancing individual autonomy and societal well-being deserves thoughtful consideration regarding use of this powerful yet controversial technique.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile
