Carrier Screening: What cards were we dealt?


When I came across this video in my Facebook newsfeed this morning, I was compelled to write about it. Carrier screening is something that I feel so passionately about, but too few people even know it exists. Stories like this family’s are an excellent reminder to me of why I discuss carrier screening with every patient, and why I try to educate other healthcare providers on offering it.

Everyone is a carrier of 3-5 genetic conditions. Being a carrier of a condition typically does not affect your own health, but does put you at increased risk to have a child with the condition. Approximately 80% of babies with genetic conditions have no family history of that disorder.  If you and your partner are carriers of the same condition, there is a 25% chance that you will have an affected child with each pregnancy. Factors like being from the same region of the world, having a shared ethnic background, or being biological relatives increase the chance that a couple will be carriers of the same thing.

The American College of Obstetrics and Gynecology (ACOG) recommends carrier screening be offered to all women who are currently pregnant or planning to become pregnant. It’s a simple test of your blood or saliva to see what conditions you may carry.  When you learn that you are a carrier of a condition, or rather, what condition(s) you carry, your partner can be tested to see if they carry the same things. ACOG’s recommendations state that at a minimum all women be offered screening for cystic fibrosis, spinal muscular atrophy, and conditions affecting red blood cells (such as sickle cell anemia). People can elect to be screened for just a few conditions to hundreds of conditions at the same time. Surprisingly, the cost is typically about the same no matter how many conditions you check for. One genetic counselor from a laboratory that performs carrier screening told me that ~3% of couples that do a large carrier screen test (known as expanded carrier screening) learn they are carriers of the same condition. On the flip side, this means 97% of couples get reassuring news from these tests.

Click here to see the ACOG recommendations!

One of the most interesting parts of my job is seeing how differently people can react to the same testing options and the reasons people have for making one decision over the other. I have some clients who think it would be crazy not to screen for everything you possibly can. The more conditions you screen for, the greater the chance you’ll find something concerning that you might want to know about. On the other hand, other clients feel screening for so many things may be a bit unnecessary. They use the same argument that the more you screen for, the greater the chance that you’re going to find something, which increases anxiety.  But wait a second… isn’t finding something the whole point of carrier screening? If you are comparing a carrier screen with 25 conditions to one with 100 conditions, what makes those 25 more important to know about than the other 75?

Many people ask me what the point is of having this information ahead of time. And again, some people think this answer is obvious and others are genuinely unsure. In my experience, the question, “What would I do with the information?” is very specific to the family AND the condition of concern. Some conditions on carrier screens are downright devastating, and people may consider altering the course of a current pregnancy or looking into other reproductive options for future pregnancies. Other conditions on the list have treatment available. Most of the time, treatment cannot reverse symptoms have are already present but can stop or slow down the progression of the disease. Knowing that a child is affected before symptoms are present can allow treatment to start as soon as possible and give them the best odds for a healthy life.

While there is no test that can screen for all conditions, we have the ability to learn if we are carriers of so many genetic conditions proactively, rather than learning only after having an affected child.  And when we know what could potentially happen, even if it’s not what we are hoping for, we are given the gift of preparation. That is where the name of my company, Family Forecast, came from. Knowing there is a high chance for thunderstorms on Tuesday may be disappointing, but at last you know to pack an umbrella.

I love to help people explore carrier screening options. Schedule an appointment with me or reach out to your physician for more information.




P.S. Exciting news! On December 23, 2016, the FDA approved the first drug to treat patients with spinal muscular atrophy, the condition in the video. The drug, Spinraza, is not a cure for the disease and still leaves much to be desired, it can halt or slow the progression of the disease. And just last month, in September 2017, the FDA approved a gene therapy clinical trial for spinal muscular atrophy.  The study will recruit a minimum of 15 patients under six months old with SMA type 1 to be given a one-time dose of the gene therapy AVXS-101. Best of luck to all the brave families participating in this trial!

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A deeper dive into genetics…

We each have two copies of each gene, one from our mother and one from our father. Genes are like recipes in a cookbook, they are a specific set of instructions to make a protein. The term “autosomal” means the responsible gene is not on a sex chromosome. Some genetic conditions occur when there is a problem in just one copy of the gene. These are known as autosomal dominant. People with autosomal dominant conditions have a 50% chance to pass it on in each pregnancy. Other conditions only occur when mutations are present in both copies of the gene. For these conditions, if a person has only one mutation they are known as a carrier and typically have no features. Some carrier screens include conditions that are “X-linked,” meaning the gene is on the X chromosomes. For these conditions, only the mother needs to be a carrier in order to have an affected child.

Options for Expanded Carrier Screening

Not all expanded carrier screens are created equal. Most of the time, your doctor’s office will select one or two expanded carrier screens that it works with. Its important to consider the number of conditions, types of conditions, testing methodology, and many other aspects of testing before you proceed. Here are links to learn more about some common expanded carrier screens.

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