Expanded Carrier Screening

When we talk about genetic risks for a future child, we tend to think mainly of the risk of accidental chromosomal anomalies. This risk is addressed by prenatal screening available in the first trimester of all pregnancies.

But what about the risk of passing on an inherited genetic condition, which cannot be identified by current prenatal screening tests?

What determines our inherited genetic risk

Unlike the risk of an accidental genetic or chromosomal abnormality at the time of conception, hereditary genetic risks can be assessed before a pregnancy occurs.

We all carry two copies of our genes, one that we inherit from our biological mother, and one from our biological father. Genetic conditions are inherited in different ways. In the case of a recessive condition, carrying a single variant is not generally associated with symptoms of the condition. But two partners who each carry variants in the same gene will be at risk of having a child with variants of both copies of the gene and will therefore be affected (symptomatic) with the genetic condition in question. There are also other possible mode of inheritance (dominant, X-linked).

Our personal, obstetric and family history

When a parent is themselves affected by a genetic condition, or when a previous pregnancy has been diagnosed with a genetic condition, it is generally recommended to be referred for genetic counselling in order to assess the risk of transmission and/or recurrence, depending on the nature of the condition and its inheritance. This is also the case if a member of our family has been diagnosed with a genetic condition that we might be at risk of carrying or developing.

Our status as a silent carrier

Although we tend to be reassured if we and our relatives are in good general health, the absence of a diagnosis of a genetic condition in our family unfortunately does not eliminate the risk of passing on a hereditary condition to our children.

We are all carriers of several silent genetic variants, often without knowing it, and regardless of our ethnic origin or family history. When two parents are silent carriers for the same genetic condition, they are then at increased risk of having a child with this condition*.

*This is the case for recessive genetic conditions. In the case of X-linked genetic conditions, a healthy woman could carry a silent genetic variant that could cause a severe genetic condition in 50% of her children, with generally greater severity for boys. 

The expanded carrier screening test

There is a private genetic test that can help identify the silent genetic variants that we carry. This test screens for several hundred severe genetic conditions that are transmitted in a recessive or X-linked manner and can be carried silently even in the absence of a family history.

Although it is possible to do this test when a pregnancy is already in progress, the best time is before a pregnancy (preconception), in order to be able to access a range of reproductive options if there is a risk identified.  This test can be performed on saliva samples from both partners of a couple, and results are usually available within two to three weeks.

Although this test is relevant for all couples who wish to have a child, there are certain situations where it could be even more beneficial, such as in the context of poor knowledge of our family history, if we belong to a population with a founder effect, such as those of Ashkenazi Jewish origin or from the Saguenay Lac-Saint-Jean region, or if the parents are related (consanguinity).

Note that couples and individuals in the fertility process who will use a gamete (egg or sperm) donor are sometimes also required to do this testing to help them in their choice of a donor.

In conclusion, the assessment of your history during genetic counselling and expanded carrier screening are valuable tools to determine your risk of passing on an inherited condition to your children. If you are identified at risk, reproductive options will be available.

If you have any concerns about a future pregnancy, do not hesitate to contact our genetic counselling service to request a consultation and assess your risks. You can also proceed directly to an extended carrier screening test (without prescription).