If you are pregnant, or are considering becoming pregnant, there are many tests available to you that can help determine your chances of having a healthy child. One such test is known as genetic carrier screening, which determines whether both you and your partner have mutations in the same gene or genes. Having mutations in the same gene would put you at risk of having children with a specific recessively inherited genetic disorder. Common recessive genetic disorders include cystic fibrosis, Tay-Sachs disease, sickle cell anemia and spinal muscular atrophy. Genetic carrier screening is not a mandatory test. If you choose to undergo genetic carrier screening, it is important that you understand both the risks and benefits of this kind of testing before having your blood drawn. Here are some points to consider when making your decision:
What is Genetic Carrier Screening?
Genetic carrier screening (GCS) is a test performed on a blood or saliva sample that determines whether a healthy person is a carrier for one or more genetic disorders. A carrier is someone who has a mutation in one gene of a pair. Carriers are typically healthy, because the other copy of that gene works normally. A person who has two non-working copies of a gene (i.e. mutations in both copies) will be affected by a recessive genetic disorder.
What does this Mean to You?
If both you and your partner are carriers for the same genetic disorder, you have a 25% chance (with each pregnancy) of having an affected child. While all people carry a small number of recessive gene mutations, it is only when both parents carry a mutation in the same gene that they are at risk for the disorder to occur in their children. Most people only become aware that they are carriers after having a child with a genetic disorder – or by having GCS. Recent advances in technology now allow for GCS to be performed for many genetic disorders at one time for a relatively low cost. This testing may be called by any number of names, including ‘multi-disease genetic carrier screening panel’, ‘universal genetic carrier screening’, or ‘all-in-one genetic carrier screening’.
Who should Consider GCS?
Anyone planning a pregnancy can choose to have GCS. In the past, genetic carrier screening was only offered to individuals with a family history of a genetic disorder or to people at risk for specific genetic conditions based on their race or ethnicity. Most racial/ethnic groups have one or two conditions that occur more commonly within their populations. For example, cystic fibrosis is relatively common in the Caucasian population, and Tay-Sachs occurs more frequently in the Ashkenazi Jewish population. Now, with the advent of the multi-disease GCS panels mentioned in the section above, anyone who wants additional information about their reproductive risks can request carrier testing, regardless of family history or racial/ethnic background. The information you learn from genetic carrier screening can help guide your reproductive decisions, but the test cannot change your carrier status.
When should GCS be Performed?
Ideally, GCS should be performed prior to pregnancy. Screening results can help you in considering all of your reproductive options. If you are already planning to pursue in vitro fertilization (IVF), genetic carrier screening should be performed well in advance of starting your IVF medications. This allows enough time for the development of a custom preimplantation genetic diagnosis (PGD) test, if you decide to have this done. If you are currently pregnant, you should consider having genetic carrier screening performed as early in your pregnancy as possible.
What are your Options if you are Found to be a Carrier?
If you are found to be a carrier for a genetic disorder, we recommend that you speak with a genetic counselor or physician in your area to discuss your results in detail. It is important that your partner be tested for the same genetic disorder to determine whether you are at risk to have children with that condition. If tests conclude that you are at risk of having a child affected with a specific genetic disorder, there are several reproductive options available to you:
In Vitro Fertilization (IVF) with Preimplantation Genetic Diagnosis (PGD)
This procedure helps you and your IVF doctor select those embryos that are most likely to develop into a baby free of the specific genetic disorder. Use of a sperm donor who is not a carrier for the specific genetic condition
and it removes chance of passing on two non-working copies of a gene and having an affected child. Sperm donors can be used with either artificial insemination or IVF. The use of an egg donor who is not a carrier for the specific genetic condition. This procedure also removes chance of passing on two non-working copies of a gene and having an affected child. Egg donors can only be used with IVF.
Prenatal Diagnosis via Chorionic Villus Sampling (CVS) or Amniocentesis
This procedure identifies during the pregnancy whether or not a fetus is affected by the genetic disorder. Results can be used to make decisions about the pregnancy or to help prepare for the birth of an affected child.
Natural Pregnancy with Testing Performed After Birth
Avoids the small risk associated with prenatal diagnosis.
Allows you to have a family without passing on the specific genetic disorder.
How can you decide if genetic carrier screening is right for you?
Deciding whether or not to have genetic carrier screening is not easy. Many laboratories that perform genetic carrier screening have genetic counselors on staff to answer your questions about their tests and what you can expect. Genetic carrier screening can be a very sensitive and personal experience − you may experience a range of emotional responses related to your genetic screening results. Meeting with a local genetic counselor or calling the genetic counselor at the screening lab prior to testing may be helpful. A qualified genetic counselor can discuss with you:
What it Means to be a Carrier
Your physician may be able to refer you to a local genetic counselor. You can also find a counselor in your area by visiting the National Society of Genetic Counselors web site at http://www.nsgc.org.