Genetic Carrier Testing

Genetic Carrier Disease testing is a diagnostic test that can be done as a normal part of obstetric care. This test, which can be done before you conceive or during pregnancy, can tell you if you and your partner are at risk of passing along certain genetic diseases to your children that you may not have yourself.

    About Genetic Carrier Testing:

    Genetic Carrier Disease testing is a diagnostic test that can be done as a normal part of obstetric care. This test, which can be done before you conceive or during pregnancy, can tell you if you and your partner are at risk of passing along certain genetic diseases to your children that you may not have yourself.

    What is a genetic disease?

    Everyone has two sets of DNA: one from Mom and one from Dad. When a sperm (carrying Dad’s DNA) fertilizes an egg (containing Mom’s DNA), those two sets of DNA combine to make a new mixture which builds the unique genetics of your baby. Your baby’s genetics will determine your child’s hair and eye color, height, and all sorts of other traits.

    A genetic disease occurs when one or both parents’ sets of DNA have a mutation (a change from the usual), which could make a baby more prone to developing health conditions. Some mutations are harmless, some only slightly boost the risk of a condition, and others can cause more serious diseases or developmental problems that can begin at birth.

    What does it mean to be a genetic disease “carrier”?

    Just about everyone carries a gene for at least one genetic disorder even if it has never shown up in your family history. If you have a mutation in just one set of genes, you are what is known as a “carrier”: You are carrying the genes for a genetic disorder but have no signs of the disease.

    Rarely, a condition (like Huntington’s disease) can be caused by a mutation in just one set of DNA from one parent. But in most cases, including cystic fibrosis and sickle cell disease, it takes a mutation in both sets of DNA, one from Mom and one from Dad, for a child to be affected by a genetic disease. Therefore, these diseases are rare.

    How does carrier screening identify the risks?

    A carrier screening tests whether you or your partner is a carrier for certain genetic diseases. It is a swab test, which requires a quick swab on the inside of your cheek. If both you and your partner are carriers, and you both pass the mutation-carrying DNA along to a baby, the baby could end up with a full-fledged version of the disease. This test determines the likelihood of this happening.

    Who is a candidate for this testing?

    Parents can be tested for some of genetic disorders before (which is preferable) or during pregnancy, thanks to genetic testing. In almost all cases, testing is recommended for one parent. Testing the second parent only becomes necessary if the first tests positive.

    In the past, the American Congress of Obstetricians and Gynecologists (ACOG) only recommended carrier screenings to parents of certain ethnic or geographic backgrounds considered more at risk of specific disorders. However, some conditions are not limited to one ethnicity. Today’s environment we have many people are of mixed ethnic backgrounds, which means it can be hard to make recommendations based on an ethnic or geographic basis. Although they are still very rare, some genetic conditions are common enough that practitioners should offer to screen for them in every patient. 

    Because some people are more likely to carry specific genetic mutations, your doctor may recommend a number of other screenings based on your family heritage and/or medical history:

    • Eastern and Central Eastern (Ashkenazi) Jewish descent: Tay-Sachs disease, Canavan disease and familial dysautonomia; there are several other disorders some practitioners screen for including Bloom syndrome, Maple syrup urine disease and Niemann-Pick disease, among others
    • French-Canadian or Cajun: Tay-Sachs disease
    • Ovarian insufficiency syndrome: Fragile X syndrome; the screening should also be offered to women with a family history of fragile X-related disorders
    • Other family history of disease: Anyone who has a family history of genetic diseases such as a cousin who had Tay-Sachs disease, for instance, should be screened for those diseases as well, as they’re more likely to be a carrier

    What is expanded carrier screening?

    Expanded carrier screening now enables all couples, regardless of their ethnic or geographical profile, to test for a broad array of genetic conditions before conceiving. It can screen for the carrier gene of hundreds of diseases, giving you the power of knowing whether you and your partner are at risk of passing along any of these genetic conditions to a baby you conceive together.

    ACOG has specific recommendations for which disorders practitioners should include in an expanded carrier panel. Conditions should occur in at least 1 in 100 people, reduce the quality of life, impair cognitive or physical abilities, require surgical or medical intervention, and have an onset in childhood. Here are a few of the most common diseases expanded carrier screenings test for:

    • Alpha-Thalassemia
    • Beta-Thalassemia
    • Cystic Fibrosis
    • Familial Hyperinsulinism
    • Fanconi Anemia Group C
    • Fragile X Syndrome
    • Gaucher Disease
    • Glycogen Storage Disease Type 1a
    • Maple Syrup Urine Disease Type 1A/1B
    • Neimann-Pick Disease Type A/B
    • Sickle Cell Disease
    • Spinal Muscular Atrophy (SMA)
    • Tay-Sachs Disease

    If you’re interested in testing for specific diseases, talk to your practitioner about your and your partner’s risk factors, as well as how you’ll use the information about each disease. If you have further questions, a conversation with a genetic counselor can be helpful.

    Before You Get Carrier Screening

    Before You Get Carrier Screening

    Both ACOG and the American College of Medical Genetics and Genomics (ACMG) agree that all couples should be offered the option of carrier screening, should they choose. To reduce the potential emotional downside of screening, experts recommend that couples have a discussion with an OB/GYN and/or genetic counselor before getting the testing to make sure they understand what is being tested for. Any discussion about carrier screening should also include a conversation about what you would do if these results come back positive. You can choose to opt-out of any or all carrier screenings or request not to receive certain results. Ultimately, it’s up to you and your partner to make an informed decision about what’s best for you and your soon-to-be growing family.

    When is carrier screening done?

    Genetic carrier screening can be done when you are just in the planning stages of starting a family, while you are actively trying to conceive or once you have gotten a positive pregnancy test. That said, if you are interested in the test, the earlier you get it done, the more likely doctors can do something if they do detect that you’re carrying a mutation.

    How is it done?

    Once a sample of your cheek cells is taken, DNA will be isolated in a lab from these cells. This allows for any mutations that are being tested to be detected.

    What are the odds of our baby having a disease if we test positive?

    Even if both you and your partner test positive as carriers of the same genetic mutation, there’s still only a 1 in 4 (or 25 percent) chance that your baby will have the disease. That’s because each of you has two sets of DNA. Since you are carriers and do not actually have the disease, that means you each have a second, healthy copy. If the baby inherits the healthy copy from one or both of you, he will not have the disease (although your child may be a carrier).

    Is there anything we can do if we test positive?

    The most powerful time to get information from carrier screening is before you’re pregnant. If you and your partner do test positive as carriers of a genetic disease, you may choose to work with fertility doctors to discuss your options.

    If you get a carrier screening done after you are already pregnant, a positive result can mean more tests to see whether your baby is affected. A positive result on one of these tests can be valuable to help you think ahead and plan financially. It could also lead to early treatments for the disease before the baby is born as well as arrange for special care during and after birth.

    And since genetic disorders do tend to run in families, ACOG suggests that you should inform relatives of positive results so they can decide whether they would like to be screened as well.

    Genetic Counseling

    Even if you don’t talk to a genetic counselor before proceeding with carrier screening, many health care practitioners will refer you to one to help you interpret your results and decide what to do with any information you obtain. As more and more tests become available, understanding what they mean can be confusing and genetic counselors are trained in helping you sort through the available information to make sense of it.

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