All about targeted vs. expanded carrier screening, the ideal time to get tested, and how to decide if it’s right for you.

 

By Liz Kane, PhD

Genetic carrier screening is a test that prospective parents can take to learn more about the genetic health of their future biological children. We’ll talk you through how it works, why some couples choose it and others don’t, and what it can and can’t tell you.

What’s Genetic Carrier Screening? 

This is a genetic test, meaning it looks at the genes of each partner. What are genes exactly? They are the building blocks of your DNA, the instructions inside each cell that contain the blueprint for making who you are. Each parent contributes half of their genetic material to their child, so if you know the genetic background of each parent, you can infer the potential genetic makeup of their children.

Let’s go back to biology class for a minute. You have two copies or variants of every gene (one from each of your parents) that encode a particular trait. These two copies can be of different types. If a trait is Mendelian, named for the Austrian monk, Gregor Mendel who created the science of genetics in the 1850s, these two gene variants are called dominant and recessive. Cleft chin, cheek dimples, and hitchhiker’s thumb are all examples of Mendelian traits. 

Image of Gregor Mendel

Image of Gregor Mendel.

If you have one copy of the dominant variant of a gene, even if the other copy is recessive, the dominant variant will hide the recessive variant, and its version will be “expressed” or shown. In order to find any recessive or other types of “silent” variants of genes, you need to take a test that can look at your actual DNA, like a genetic carrier screen.

The word “carrier” in "genetic carrier screen” refers to these silent gene variants that you may be carrying but not know. In this case, genetic carrier screens are looking for these gene variants that would cause disease if a child inherited two copies from both their parents. The exact chance that the child will be affected depends on the disorder. 

Is Genetic Carrier Screening for Me?

If you feel that genetic carrier screening is right for you, talk about it with your doctor or OBGYN. A good time would be at your preconception visit before you start trying to conceive. It can be helpful to have this information in order to plan ahead for pregnancy and birth and to discuss with your partner how you plan to proceed.

It’s also important to consider if just one, or both partners, should pursue testing. If one partner pursues testing first, the other may need to get testing if the first partner’s results come back positive. This may be the most prudent path if you are paying for testing out of pocket. If your testing is covered by insurance, pursuing testing for both partners at the same time is the quickest way to get all the information you need.   

If your preventative genetic testing comes back positive for a condition, talk to your doctor about your options. If you know this information ahead of time, you may use assisted reproductive technology to get pregnant with an embryo that doesn't carry the genetic disorder. Genetic carrier screening isn’t for everyone, and some people decide that they’re not interested in pursuing it at all. Either path is a complicated and personal decision that involves deciding what’s important to you, and what you would do with that information.

Personally, my husband and I chose to pursue genetic carrier screening at the same time. We both are of Ashkenazi Jewish ancestry, making it likely we would be carriers for the same genetic conditions (more on that below). We are both people who prefer to know as much information as possible before we make a decision, so pursuing genetic carrier screening before pregnancy was the right decision for us. Talk with your doctor to determine what is the best path forward for your family. 

How Many Diseases Will I Be Screened For?

In short, that’s up to you. ACOG recommends that all women be offered screening for cystic fibrosis (a disorder that affects the lungs) and spinal muscular atrophy (SMA) (a disorder that causes muscle wasting and weakness). Beyond that, additional screening is available in two forms: targeted and expanded.

  1. Targeted carrier screening is testing based on your ethnicity and family history. People of certain ethnicities are more likely to be carriers of particular disorders, such as Tay-Sachs disease in Ashkenazi Jews, sickle cell anemia in African Americans, and blood disorders (thalassemias) in Southeast Asians and people of Mediterranean descent. Another sign that you may want to pursue expanded screening is a family history of a genetic disorder, which makes it more likely that you could be a carrier for a genetic disorder.
  2. Expanded carrier screening tests for a greater range of genetic disorders—most for over 100. These tests are a thorough search of almost all known genetic disorders. While it can seem like more information is better, expanded screening can yield results that don’t always provide a perfectly clear path forward. For example, some carrier statuses do not definitively cause disease but instead influence the likelihood of a child developing a condition later in life (like BRCA1/2 and certain cancers). Additionally, the chances of an expanded test coming back positive are much higher than the targeted one. Precision medicine (medicine based on a person’s genetics) is at the forefront of clinical research, and that means there’s much that we don’t yet understand. If you do seek expanded screening, make sure you also receive genetic counseling to help you understand your results.

Will My Insurance Cover Carrier Screening?

As is always the case with health insurance, the answer is it depends. If your doctor recommends and orders the targeted screening, then it’s often, but not always, covered by health insurance. It’s best to talk with your doctor and insurance company first to find out.

What Happens to My Genetic Data?

This is a new frontier, and the government has yet to establish privacy and ownership policies around genetic information. Keep in mind that genetic information is incredibly valuable to researchers and for-profit companies. If you choose to have genetic carrier screening, make sure that you know and are comfortable with how your data will be used after testing. Don’t be afraid to ask the company directly. 

Some people fear that their insurance provider will increase rates if they find out a member carries a disease risk, but in the US this is illegal under the Genetic Information Nondiscrimination Act. Note that this law does not apply to providers of life, disability, or long-term care insurance.

Seek Help If You Need It

If you’re wrestling with these questions—whether or not to seek testing, or what to do with the test results—there are people available to help you. Your doctor can connect you with a mental health professional or a genetic counselor. If you need help, we urge you to ask for it—these questions are complicated, and you don’t need to answer them alone.

Do you have more pregnancy-related questions? See additional resources here.

 

Featured image details: X-ray crystallographic photo of DNA taken by Rosalind Franklin in May 1952 during the race to find the structure of DNA. Rosalind Franklin was the only woman lead scientist participating in the race. Unfortunately, she passed away before the Nobel Prize in Medicine (likely from cancer acquired from radiation during her experiments) was awarded to Watson and Crick for discovering the structure of DNA, which made her ineligible to receive it. Image credit.