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Genetic Testing Dilemmas

  • By Peter Tyson
  • Posted 03.08.12
  • NOVA

Scenario 1: Testing Embryos

You and your husband are about to start a family. Your husband has a genetic mutation that greatly increases his chances, sometime in his life, of getting a rare form of colon cancer, a type that killed his mother and an uncle. Preimplantation genetic diagnosis, or PGD, makes it possible to test your embryos for the mutation and transfer only those that do not have it into your uterus to continue development. PGD involves removing one of eight cells in an embryo that, if deemed healthy, is transferred back into you for development—minus that one cell. However, even if you don't do PGD and your baby were to inherit the mutation, there is no certainty that he or she would later get the disease.

Embryo under a microscope

Given the above information, would you get tested?

Once you make this initial choice, you will have a chance to review some key issues that people typically consider. Then you can choose again—and see how others felt.

Now consider the following and then decide again afterwards:

PGD can help parents avoid passing on mutations

Some who know they have a mutation that increases their chances of contracting a deadly disease want to make sure that their unborn children do not inherit it:

"I couldn't imagine them [later] telling me my daughter has cancer, when I could have stopped it [when she was at the embryo stage]." —Chad Kingsbury, who has a genetic mutation that makes him susceptible to an inherited form of colon cancer, and decided, with his wife Colby, to do PGD; as a result, their daughter Chloe does not have the misspelled gene.

to some, PGD smacks of eugenics

To some people, even if they have a dreaded mutation, PGD seems like a kind of eugenics—the now-repudiated policy of past governments, in the U.S. and elsewhere, to prevent certain people from reproducing because they were considered genetically inferior:

"It's like children are admitted to a family only if they pass the test. It's like, 'If you have a gene, we don't want you; if you have the potential to develop cancer, you can't be in our family.'" —Denise Toeckes, a 32-year-old teacher who tested positive for a mutation that increases her chances of developing breast cancer

some use PGD to create "savior siblings"

Some couples have begun turning to PGD to help them have a baby that could provide a cell transplant to treat a desperately ill older sister or brother:

"You could say it was an added perk to have Adam be the right bone marrow type, which would not hurt him in the least and would save Molly's life. We didn't have to think twice about it." —Lisa Nash, who used PGD with her husband to find an embryo that would not have the deadly blood disease Fanconi anemia that her six-year-old daughter Molly has, and would also be a tissue match for Molly. The chosen embryo became her son Adam, whose umbilical-cord blood cells were used to successfully treat Molly.

PGD's success rate is not perfect

Some worry about PGD's failure rate, which is up to 5 percent:

"You feel so guilty because you're trying to help one daughter and you end up hurting two other children. Now we understand that it's not an exact science and there's room for error." —Doreen Flynn, 29, who did PGD with her husband to find embryos free of Fanconi anemia, which their young daughter has. Two selected embryos became two more daughters, who, despite PGD, were born with the disease.

Are you ready to decide again about whether you would want to get embryos tested before you have a baby?

Remember, there are no right or wrong answers, and only your choice will be recorded, not your name or any other identifying information.

Knowing all of the above, would you get tested?

facts & figures

PGD is most commonly used for four kinds of tests. These include tests for: 1) genetic abnormalities, such as single-gene defects that cause diseases like cystic fibrosis; 2) aneuploidy—a chromosome problem, such as Down syndrome, that is caused by an extra or missing chromosome; 3) translocation, in which pieces of one or more chromosomes have switched places, causing carriers to be at increased risk of infertility, miscarriage, stillbirth, and/or having a child with birth defects; and 4) choosing the sex of the embryo.

During in vitro fertilization (IVF), after a woman's ovaries are stimulated using hormones, some eggs are extracted and fertilized in the laboratory with sperm. In PGD, a cell is removed from each of these embryos when they have reached the eight-cell stage (after three days of development). Only those embryos that are deemed healthy or of the preferred sex will be transferred into the woman's uterus for development.

Since its introduction in 1990, PGD has been widely used to prevent the development of embryos with mutations for lethal diseases such as cystic fibrosis and Huntington's chorea, and to prevent recurrent pregnancy loss.

Sources

General

Collins, Francis S. 2010. The Language of Life: DNA and the Revolution in Personalized Medicine. HarperCollins.

Davies, Kevin. 2010. The $1,000 Genome: The Revolution in DNA Sequencing and the New Era of Personalized Medicine. Free Press.

Elton, Catherine. 2009. "The Burden of Knowing." Boston Magazine. January.

Green, Ronald M. 2007. Babies by Design: The Ethics of Genetic Choice. Yale University Press.

Harmon, Amy. 2006. "Couples cull embryos to halt heritage of cancer." The New York Times, 3 September.

Zallen, Doris Teichler. 2008. To Test or Not to Test: A Guide to Genetic Screening and Risk. Rutgers University Press.

Scenario 1: Testing Embryos

"I couldn't imagine them…" Harmon (see General sources).

"It's like children are admitted…" Ibid.

"You could say it was an added perk…" Grady, Denise. 2000. "Son conceived to provide blood cells for daughter." The New York Times, 4 October.

"You feel so guilty…" Tarkan, Laurie. 2005. "Screening for abnormal embryos offers couples hope after heartbreak." The New York Times, 22 November.

Credits

The author would like to thank Doris Teichler Zallen, author of To Test or Not to Test (see Sources, General), for reviewing this feature for accuracy and for her kind permission to quote extensively from her book. Thanks also to Lars Bertram, M.D., Head of the Neuropsychiatric Genetics Group at the Max-Planck Institute for Molecular Genetics; Mary-Claire King, M.D., Ph.D., at the University of Washington School of Medicine; and Mark Hughes, M.D., Ph.D., Senior Scientist and Director at the Genesis Genetics Institute. Thanks, finally, to Mary Crowley and Josephine Johnston of the Hastings Center (www.thehastingscenter.org) for helpful comments on the text.

Producer:
Peter Tyson
Designer:
Kim Ducharme
Developer:
Daniel Hart

Images

Intro: hand with pen over DNA sequencing
Jacob Halaska/Photolibrary/Getty Images
Page 1: IVF embryo testing
Pascal Goetgheluck/Photo Researchers, Inc.
Page 2: scans of normal (right) and Alzheimer's brains
Science Source/Photo Researchers/Getty Images
Page 3: woman crossing her arms
Helen McArdle/Photo Researchers, Inc.
Page 4: close-up of DNA sequencing gel
Steven Puetzer/Photographer's Choice RF/Getty Images