A compilation of the most frequently asked questions I receive about carrier screening.
The Basics
What is carrier screening?
It’s a genetic test (usually a blood test, but also available via saliva or cheek-swab) that assesses risk of passing down genetic conditions to your children.
What exactly is a carrier?
Everyone has two copies of every gene. A carrier of a genetic condition has one healthy copy of the gene, and one copy that does not work properly.
Most of us are carriers for at least one genetic condition but would never know it without testing. Carriers generally do not exhibit symptoms or even have a family history of the condition.
How does my carrier status affect my children’s risk?
The risk to your children depends on the specific condition you carry and how it is inherited. In other words- how is this condition passed down? Carrier screening looks at two types of inheritance: autosomal recessive and X-linked recessive.
Autosomal Recessive Conditions: If both you and your partner (or donor) carry the same recessive condition, there is a 25% chance with each pregnancy that your child will inherit the condition. Examples include Cystic fibrosis and Tay-Sachs disease.
X-Linked Recessive Conditions: If you are a female carrier for an X-linked condition, each of your male children has a 50% chance of being affected, while each of your female children has a 50% chance of being a carrier. Female carriers may also experience symptoms. Examples include Duchenne muscular dystrophy and Hemophilia A.
My partner already had carrier screening and screened negative for everything. Do I still need to get tested?
It depends!
If you’re female (XX) and your male partner screened negative for all conditions, it’s still recommended that you have carrier screening to assess risk for X-linked conditions.
If you’re male (XY) and your female partner had a negative comprehensive carrier screening panel, carrier screening for you is not necessary to determine reproductive risk.
I was identified to be a carrier for a genetic condition! Does that mean I’m at risk to develop the condition myself?
Usually, no. Carriers are typically healthy and do not exhibit symptoms. However, exceptions exist. If you’re concerned about symptoms related to carrier status, review this information with a genetic counselor.
Note: your first-degree relatives (parents/siblings) are at 50% risk to be carriers for the same conditions as you. It’s best to share results with your family.
When should I get screened?
If you’re considering having (biological) children, and you want to move forward with information, it should ideally be performed before you start trying to conceive.
I often encounter patients who learn they are carriers for the same conditions during pregnancy, who wish they had this information earlier. It can help with decisions to pursue alternative reproductive options including IVF.
However, if you do learn about a carrier match while pregnant, there are still prenatal testing options available.
What do I do if I’m a carrier for the same condition as my partner?
You have options! More on this here.
The short answer? Meet with a genetic counselor!
I’m not the same ethnicity as my partner… can we still benefit from this testing?
Yes! While some conditions are more common in specific populations, they are by no means exclusive to that group. Carrier screening can be beneficial to all couples regardless of ethnicity.
There are no genetic conditions that run in my family. Is this screening still worthwhile?
Yes! The genetic conditions included on these panels most often do not run in families.
What if I’m using an egg / sperm / embryo donor? What are my options?
Egg/sperm (gamete) donation agencies often have carrier screening performed on donors. Ask for a de-identified copy of your intended donor’s genetic test results.
You can have carrier screening performed prior to selecting your donor to avoid selecting one who is a carrier match.
Have a genetic counselor review all reports.
What’s included?
What conditions are screened on carrier screening?
The majority are severe, childhood-onset conditions that can affect health, development, and/or functioning of certain body systems.
Keep in mind: there are many different carrier screening panels on the market, and they all include slightly different conditions from one another. Some offer testing for just a few diseases and some test for hundreds.
What are the different types of carrier screening, and how do I know which to choose?
Panels range from two to hundreds of conditions (with lots of in-between.) Since I believe knowledge is power, I prefer panels that cover 400+ genetic conditions, including the conditions recommended by the American College of Medical Genetics and The American College of Obstetrics and Gynecology.
I also favor panels that use a comprehensive technology called gene sequencing with copy number variant analysis (which gives us an in-depth view of the genes analyzed), rather than common mutation analysis (which can miss rare variants).
Are the BRCA genes (and other cancer predisposition genes) included on my carrier screening panel?
Cancer predisposition genes are most often not included on carrier screening panels. (A few exceptions to this rule exist.)
These conditions are often adult-onset and can be inherited in a dominant manner, while carrier screening focuses on childhood-onset conditions inherited in autosomal recessive and X-linked inheritance patterns.
Cancer-predisposition genetic testing is a separate test that can also provide valuable information.
Limitations
Does carrier screening include every single genetic condition?
No. No matter which carrier screening panel you’ve had, it includes only a subset of autosomal recessive and X-linked conditions.
My partner and I already had carrier screening years ago, and weren’t identified to be carriers for any of the same conditions. Do we need to repeat this testing?
While our carrier status never changes (it’s literally in our DNA), the carrier screening panels become more comprehensive over time. You might learn that you now have access to screen for many conditions that you haven’t already tested, or that your specific genetic variants have been re-classified. It’s best to review your previous results with a genetic counselor to discuss next steps.
What might I learn from carrier screening in addition to carrier status?
The purpose of carrier screening is to assess your reproductive risks. Rarely, you can learn personal risk factors from your carrier status. Additionally, you can sometimes learn you have a mild form of one of the conditions included on your panel.
For example, carriers for some conditions may be at an increased risk to develop certain cancers. If this is the case, your genetic counselor will assist you with next steps.
Please note: carrier screening should not be treated as a comprehensive genetic screen for risk to develop adult-onset conditions like cancer.
My partner and I aren’t carriers for the same conditions…does that mean there is zero risk for these conditions?
In genetics, we can never use the word zero. But it does mean your risk for those conditions is reduced. Often, a laboratory will provide a residual risk for each condition on the lab report or website.
It’s best to make sure your panel includes good coverage of the genes tested. Ask your ordering provider if your screen includes gene sequencing with copy number variant (CNV) analysis.
Access
How can I get carrier screening?
Reach out to an OBGYN, or find a local genetic counselor.
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Excellent, easy to understand piece!