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Code Check

Genetic testing can reveal if you or members of your family tree are predisposed to disease or birth defects. But basing health-care decisions on such information isn’t always clear-cut: DNA isn’t necessarily destiny.

Code Check
Photo by Harry Campbell (Illustration)

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The Price of Knowledge

Genetic tests can help couples weigh whether to have children. But the hardest decision is often whether to get tested at all.

The pre-wedding to-do list of Christina Schlemmer, 25, includes the usual tasks: Mail the invitations. Make sure the bridesmaids get fitted for their gowns. Double-check the honeymoon reservations.

But also on this bride-to-be’s list is an item rarely suggested by professional wedding planners: schedule a genetic-testing appointment for the fiancé.

Schlemmer, of St. Paul, has cystic fibrosis (CF), an incurable genetic disease that affects breathing and digestion. Just a few decades ago, few children with CF lived past their elementary-school years. Today, thanks to new treatments, many people with CF lead active, productive lives into their thirties, forties, and beyond.

Those same medical advances have made it possible for some women with CF to have successful pregnancies. Schlemmer, whose CF symptoms are relatively mild, hopes to have two or three children.

Genetic testing will help her and her fiancé prepare for parenthood, says Schlemmer, especially if the children have CF. The disease is not always passed on from mother to infant. For a baby to be born with CF, both parents must carry a copy of the defective CF gene. If her fiancé, Nick Doffing, is one of the 10 million Americans who are symptomless carriers of the defective CF gene—as both Schlemmer’s parents are—any child born to Doffing and Schlemmer would have a 50-50 chance of having CF.

Screening for genetic carriers has grown in recent years. CF tests are now routinely offered to all couples planning a pregnancy, not just those with a family history of the disease. Other common genetic tests given to prospective parents include those for sickle cell anemia, muscular dystrophy, and Tay-Sachs disease.

Photo by Eric Moore

“Many couples have genetic testing because they want information, but they may be very unsure at that point what they want to do with it,” says Noralane Lindor, MD, a professor in the genetics department at the Mayo Clinic College of Medicine.

Undergoing genetic counseling before gene screening can help couples decide whether they even want the information. “One of the major misconceptions I encounter is that we’re always pushing people to do the testing,” says Matt Bower, a genetic counselor at the University of Minnesota Medical Center–Fairview. That’s untrue, he says. “I’ve had innumerable instances where I’ve helped people decide that testing really wasn’t in their best interest,” he says.

If a prenatal test comes back positive for a genetic disorder, some women use that information to prepare themselves emotionally and otherwise to care for a child with a disability. Others, however, choose to end the pregnancy.

Schlemmer says that even if Nick is a carrier of the CF gene, it will not affect the couple’s choices. “It won’t matter,” she says. “I was three months old when my parents found out that I had CF. I just think it would be better to know from the start.”

Common Genetic Screening Tests

MANY GENETIC DISORDERS are autosomal recessive—passed on to children only if both parents are carriers of the genetic trait for that disorder. But if the parents themselves exhibit no manifestations of the disorder, genetic testing is needed to determine whether they are carriers. If tests show that both parents are carriers of a particular defect, they may opt for prenatal testing to determine if their fetus has the disorder. Children of two carriers have a 25 percent of inheriting the disorder.

The following are some of the autosomal recessive disorders that prospective parents are often tested for. Some genetic disorders are more likely to occur among people of particular racial and ethnic backgrounds.

Parents of African Background

• Sickle cell disease (carrier frequency: 1 in 12)

Parents of Ashkenazi Jewish Background

• Tay-Sachs disease (carrier frequency: 1 in 30)
• Canavan disease (carrier frequency: 1 in 40)
• Niemann-Pick disease type A (carrier frequency: 1 in 90)
• Gaucher disease type 1 (carrier frequency: 1 in 12)
• Bloom syndrome (carrier frequency: 1 in 100)

Parents of Caucasian Background

• Cystic fibrosis (carrier frequency: 1 in 25)

Parents of Mediterranean (Greek, Italian), Southeast Asian, and/or African Background

• Beta-thalassemia (carrier frequency varies with ethnic group)

Parents of Southeast Asian Background

• Alpha-thalassemia (carrier frequency varies, but may be as high as 1 in 20)

DNA 411

Questions and Answers Regarding Gene Screening

What kinds of genetic tests are available?
There are more than 1,000 genetic tests, which fall into several categories. Carrier screening determines if you (and/or your partner) carry a gene mutation for a disease that could be passed on. Prenatal diagnostic testing determines whether a fetus has a genetic disorder. Predictive testing helps you estimate your risk of developing hereditary disorders, such as some forms of breast cancer. If you’re already displaying symptoms of a genetic disease, diagnostic testing will help confirm that you have the disorder.

Who are genetic counselors?
They’re specialized health professionals who have completed a master’s program in medical genetics and counseling skills and who have been accredited by the American Board of Genetic Counseling. In addition to knowing the benefits and limitations of genetic screening, the counselors can help navigate emotional and ethical issues.

How do I find a genetic counselor?
The best way is to ask your physician for a referral. You can also locate a genetic counselor through the National Society of Genetic Counselors’ website: www.nsgc.org/resourcelink.cfm.

If I seek counseling, will I automatically be tested?
No. The decision to undergo genetic testing is very personal. Most genetic counselors recommend that you ask yourself what you would gain by being tested. Would you do anything differently if you discovered you carry a genetic mutation?

What does genetic testing involve?
For most genetic testing, you’ll be asked to give a small sample of blood, but cells from your hair, skin, or other tissues may also be used. For prenatal testing, cells are retrieved from amniotic fluid (amniocentesis) or the placenta.

Do the tests have any medical risks?
Prenatal testing poses a very small risk of miscarriage—no more than 1 percent, or 1 in 100 for CVS and perhaps as low as 1 in 1,600 for amniocentesis, according to new research. You’ll need to decide whether that risk is acceptable.

Susan Perry is a freelance writer who specializes in medical topics. She lives in Minneapolis.

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