Preimplantation Genetic Diagnosis

Preimplantation genetic diagnosis (PGD) is a genetic technology that allows parents to choose embryos that are a desired gender or free of a specific genetic disease. It is becoming a powerful tool for people to choose the genetic characteristics they want or, more importantly, don’t want in their children. First used in 1989,¹ to test embryos for genetic disorders, PGD is a unique blend of assisted reproductive technology and genetic technologies. The blending of these two technologies is often given the name “reprogenetics.” We will examine the technique used, the limitations of PGD, and questions parents should consider before choosing PGD.

The Technique

Normally, PGD is used with in vitro fertilization (IVF). A popular technique for parents unable to conceive naturally, the IVF process involves fertilizing an egg outside of the womb and then implanting the embryo in the mother’s uterus. Preimplantation genetic diagnosis is done after the egg and the sperm have been joined to form an embryo but before the embryo is placed inside the mother. One cell from the tiny, 6-10 cell embryo is removed and the DNA contained in that cell is tested for genetic abnormalities. The actual process of removing one of the cells usually does not harm the embryo or threaten its development. After testing the embryos, parents can choose the disease-free embryo(s) for implantation in the mother’s womb. The genetically abnormal or undesirable embryos are then destroyed.

As of September 2002, there were more than 1000 babies born as a result of this technology.² Its popularity is growing and it will soon become more available to parents who would like to use this new option in genetic technology.

Currently, PGD can be used to test for a number of genetic diseases, including:

• Alzheimer’s disease

• Hemophilia

• Muscular dystrophy

• Phenylketonuria (PKU)

• Tay-Sachs disease

• Huntington disease

• Down syndrome (and other chromosomal abnormalities such as Trisomy 18)

• Cystic fibrosis

• Fanconi’s anemia

• Turner’s syndrome

PGD can also be used to determine the gender of the child. Unlike testing for a specific disease, to test and select an embryo based on its gender could be considered a form of genetic enhancement. It's important to understand that PGD cannot genetically alter an embryo to give it desired physical or mental characteristics. However, the option of gender selection opens the door to public acceptance of more invasive methods of genetic enhancement. For more information on genetic enhancement, see Frequently Asked Questions: Genetics

Limits of Preimplantation Genetic Diagnosis

Despite its popularity, PGD has no purpose other than to screen and choose embryos based on their desired genetic material: ³

• PGD does not identify diseases that do not have a clear and simple genetic component. Nor does it recognize diseases that are known to have complex interactions between genes and the environment.

• PGD does not have any therapeutic benefits – it cannot create or change any of the genetic characteristics or abnormalities that an embryo has inherited from its parents.

• PGD does not allow parents to enhance their children’s genetic code in order to “custom-make” them with specific mental or physical characteristics.

Ethical considerations for those considering Preimplantation Genetic Diagnosis

If you have the option of using PGD, consider:

• How will you use the information you receive from the diagnosis?

• If your baby has a severe or life-threatening disorder, will you discard that embryo (the equivalent of abortion at an earlier stage of life)?

• If you are not ready to discard embryos/children based on test results, will PGD give you an advantage over being uninformed of your child’s genetic makeup?

Dawn Vargo is an associate analyst of bioethics in the Public Policy Division of Focus on the Family.