What is PGD?
Preimplantation genetic diagnosis (PGD) is an advanced reproductive technology that allows embryos created through in vitro fertilization (IVF) to be tested for genetic defects and chromosomal abnormalities prior to implantation in the uterus. During a normal PGD cycle, eggs are retrieved from the ovaries and fertilized with sperm in a laboratory. After fertilization, one or two cells are removed from embryos at the six-to-eight-cell stage for genetic analysis. The cells biopsied at this early stage do not damage the embryo’s ability to develop.
DNA from the biopsied cells is then analysed for genetic disorders and chromosomal problems. Only healthy, unaffected embryos are selected for transfer back into the uterus in the hopes of establishing a successful pregnancy. PGD aims to select the embryos least likely to be affected by the genetic conditions being tested for, rather than attempting to “repair” or alter embryos in any way.
What genetic conditions can PGD test for?
PGD can test for hundreds of single-gene disorders and chromosomal abnormalities. Some of the most common genetic conditions it can evaluate embryos for include:
– Cystic fibrosis – An inherited disease that causes severe damage to the lungs and digestive system. It is one of the most common lethal recessive disorders in Caucasians.
– Huntington’s disease – A fatal neurodegenerative disorder with no cure. It causes progressive breakdown of nerve cells in the brain. Onset is usually during middle age.
– Fragile X syndrome – The most common form of inherited intellectual disability and a leading genetic cause of autism. It results from a mutation on the X chromosome.
– Tay-Sachs disease – A rare, fatal genetic disorder that progressively destroys nerve cells in the brain and spinal cord. It mostly affects those of Ashkenazi Jewish descent.
– Trisomy 21 (Down syndrome) – A chromosomal condition associated with physical and intellectual disabilities. Risk increases dramatically with the age of the mother.
How has PGD expanded fertility treatment options?
By allowing for genetic testing of embryos before implantation, PGD has given hope to many patients and families at high risk of passing on genetic diseases. Couples that may not have considered having biological children due to inherited conditions now have the option to conceive a healthy pregnancy through IVF and PGD.
It also provides an alternative to prenatal diagnosis (PND) with abortion as the only option if an affected fetus is identified. With PGD, embryos can be tested and only unaffected ones transferred, eliminating the need for difficult decisions around terminating an established pregnancy. For diseases with no cure or effective treatment, PGD may be the only way for some families to have biologically related, unaffected children.
Are there any limitations or controversies around PGD?
While life-saving for many families, PGD does raise some ethical concerns that require ongoing discussion and oversight. There are limitations to the technology as well:
– Accuracy of testing – Although testing methods continue to improve, genetic tests used in PGD are not 100% definitive and errors or missed diagnoses can still occur in a small percentage of cases.
– Eugenics – Some critics argue PGD could enable a “designer baby” mentality and lead down a slippery slope towards attempts to screen for or select for traits unrelated to disease, like intelligence or athletic ability. Strict regulation aims to prevent this.
– Gender selection – PGD allows for selecting embryos of a desired sex, but permitting it solely for social reasons like balancing a family with children of both sexes remains controversial in some societies and is banned in many jurisdictions.
– Accessibility – PGD significantly increases the costs of IVF, putting it out of reach for many families without insurance coverage or means. Guidelines seek to prioritize its use for preventing serious inheritable conditions.
The future of PGD
As genetic science advances rapidly and preimplantation testing methods become ever more precise and extensive, PGD will likely play an expanding role in reproductive medicine. Efforts continue to make it accessible to more individuals and couples worldwide. Genetic counseling guidelines also aim to ensure its ethical application focused strictly on medical need, not non-medical traits or preferences. With prudent oversight and limitations, PGD has great potential to alleviate suffering from inherited disease for generations to come.
In Summary, Preimplantation genetic diagnosis (PGD) stands as a revolutionary technique in reproductive medicine, offering couples undergoing in vitro fertilization (IVF) the ability to analyze embryos for genetic traits before implantation. By scrutinizing embryos for specific genetic characteristics or chromosomal abnormalities, PGD provides invaluable insight into the genetic health of embryos, enabling couples to make informed decisions about their fertility treatments and family planning.
