What is Carrier Screening?
An interview with Dian Myles Reid, Genetic Counsellor at Markham Fertility Centre
On EP29 of My Fertility Podcast, we had the pleasure of hosting Diane Myles Reid, Genetics Lead at Markham Fertility Centre and President of the Canadian Association of Genetic Counsellors. In this engaging conversation, Diane unraveled the science and significance of carrier screening—an important yet often overlooked component of family planning. Let’s dive into this far-reaching discussion!
Learn more about the Genetics Program at MFC.
What is carrier screening?
Welcome, Diane! We’re thrilled to have you here. Carrier screening is a fascinating yet complex topic. Can you start by explaining what is carrier screening and why it’s important?
Diane: Absolutely, and thank you for having me! Carrier screening is a genetic test that identifies whether someone is a carrier of one or more genetic conditions. This test focuses on uncovering potential risks for passing genetic conditions to children. By identifying these risks early, individuals or couples can make informed decisions about their family planning journey.
The Foundation of Genetics
Let’s revisit the basics for clarity. What does it mean to be a “carrier,” and how does this relate to our genetics?
Diane: That’s a great question. Every cell in our body is built from instructions contained in our genes, which are inherited from our parents. Genes come in pairs—one from each parent. A “carrier” is someone who has one normal, functional copy of a gene and one altered copy, often referred to as a variant.
Carriers typically don’t experience health issues because the normal gene compensates for the altered one. However, if both partners in a couple are carriers of the same genetic condition, there’s a 25% chance their child could inherit two non-functional copies, leading to the development of that genetic condition.
What Conditions Can Carrier Screening Detect?
What kinds of genetic conditions are included in carrier screening?
Diane: The conditions we screen for vary widely. At Markham Fertility Centre, our expanded carrier screening test evaluates over 600 genetic conditions. These range from inherited forms of hearing or vision loss to neurological disorders and developmental delays. The severity of these conditions can differ significantly—some are relatively mild, while others may profoundly impact a child’s health or development.
The ability to screen for so many conditions has advanced rapidly, thanks to improved genetic understanding and technology. Each laboratory may offer different panels, so it’s important to discuss the specific conditions covered by your screening test.
The Prevalence of Genetic Carriers
How common is it for someone to be a carrier of a genetic condition?
Diane: It’s actually very common. Studies suggest that most people are carriers of two to eight genetic conditions. However, being a carrier doesn’t necessarily mean that there’s an immediate risk to your child. The risk primarily arises if both partners are carriers for the same condition, which underscores the importance of testing both individuals in a couple.
Carrier screening focuses on a subset of our genes—those associated with childhood health conditions—so it’s not an exhaustive test of all 20,000 human genes. Nonetheless, the conditions included are those most likely to affect a child’s health or development.
Who Should Consider Carrier Screening?
Is carrier screening something everyone should consider, even those with no family history of genetic conditions?
Diane: Absolutely. Most children born with genetic conditions have no prior family history of those conditions. Carrier screening is for anyone planning to start or grow their family. It’s an optional test, but it’s a powerful tool for understanding genetic risks and planning accordingly.
Expanded Scope in Donor and Surrogacy Cases
What role does carrier screening play for individuals using donor eggs, sperm, or surrogates?
Diane: Carrier screening is particularly important in these cases. Donors often undergo genetic testing, but the extent of their screening varies depending on when and where it was performed. At Markham Fertility, we ensure thorough screening for fresh egg donors to minimize risks for the intended parents and the future child.
If a donor is found to be a carrier for a specific condition, the recipient can undergo testing to determine if they’re a carrier for the same condition. This ensures that any potential risks are identified and managed proactively.
Managing Results: Next Steps for Couples
If both partners are carriers for the same condition, what happens next?
Diane: This is a critical juncture where genetic counselling becomes invaluable. We provide detailed information about the condition, including its impact on a child’s health and development. Couples are presented with several options, including:
- Preimplantation Genetic Testing for Monogenic Disorders (PGT-M): During an IVF cycle, embryos can be tested for the condition. Only unaffected embryos or those with low risk are transferred.
- Prenatal Testing: Couples may opt to conceive naturally but use testing during pregnancy to determine whether the fetus is affected.
- Exploring Donor Options: Couples may choose donor sperm or eggs to eliminate the risk of passing on the condition.
Deep Dive into PGT-M and PGT-A
Can you explain the difference between PGT-M and PGT-A?
Diane: Of course. PGTM, or Preimplantation Genetic Testing for Monogenic Disorders, focuses on identifying specific genetic conditions in embryos when there’s a known risk. PGTA, or Preimplantation Genetic Testing for Aneuploidies, screens embryos for chromosomal abnormalities that might affect implantation or pregnancy success.
These tests can be performed on the same embryo sample, but they serve distinct purposes. For example, PGTA determines whether an embryo is viable for pregnancy, while PGTM identifies whether an embryo carries a specific genetic condition.
Some couples choose to perform these tests sequentially—for instance, starting with PGTA to ensure embryos are viable before proceeding with PGTM.
The Practicalities of Carrier Screening
What does the process of carrier screening look like for someone interested in testing?
Diane: At Markham Fertility, we aim to make the process as seamless as possible. Patients can book a consultation with one of our genetic counsellors to discuss their questions and organize testing. Testing can be done via blood draw, cheek swab, or saliva sample, depending on convenience. Samples are then sent to a U.S-based lab, with results typically returning in about three weeks.
For individuals not affiliated with our clinic, carrier screening can be arranged through family doctors, independent genetic counselors, or via referral to a medical geneticist.
Carrier Screening Costs and Considerations
How much does carrier screening typically cost, and is it covered by insurance?
Diane: At our clinic, the cost is currently $520 per person, though this may vary over time and across providers. Unfortunately, carrier screening is not usually covered by insurance as it’s considered an elective test. However, it’s a valuable investment for those seeking peace of mind and clarity about their family’s genetic future.
Looking Ahead: The Future of Carrier Screening
Carrier screening seems to be gaining traction. Where do you see this field heading in the next 20 years?
Diane: Carrier screening is likely to become more common and accessible as our understanding of genetics grows. In the U.S., it’s already standard practice in many fertility clinics, and I anticipate Canada adopting similar guidelines. As testing becomes more affordable and comprehensive, I expect it to become a routine part of family planning, helping more couples make informed decisions.
Who Should Consider Carrier Screening?
Carrier screening empowers individuals and couples with critical insights into their genetic makeup. By understanding the risks of passing on genetic conditions, they can plan their family-building journey with confidence and clarity.
For those using fertility treatments, donor gametes, or surrogacy, carrier screening offers additional layers of security and understanding, ensuring every decision is made with the best available information.
Conclusion
Diane Myles Reid’s insights highlight the transformative potential of carrier screening in modern fertility care. This technology not only helps identify potential risks but also equips individuals and couples with the tools to navigate those risks effectively.
Whether you’re just beginning your family planning journey or exploring fertility treatments, carrier screening is a powerful step toward building a healthy future.
Stay tuned for our next episode, where Diane will discuss prenatal testing options and other genetic insights.
This blog captures the essence of our discussion with Diane Myles Reid and underscores the importance of carrier screening in creating a healthier future for families. Share this with anyone embarking on their journey to parenthood!