Reproductive genetic risk and expanded carrier screening
We know that all individuals carry multiple silent genetic variants even in the absence of a family history. If two biological partners carry variants for the same genetic condition, there will be a 25% (1 in 4) chance for their children to have the genetic condition in question. It can be said that the person providing the sperm and the person providing the eggs would therefore be “compatible” if the genetic variants they carry are in genes for different conditions. These risks exist for all conceptions, natural or not.
The expanded carrier screening test is a private test that looks for genetic variants in more than 500 genes associated with recessive or X-linked genetic conditions. Since the goal is to assess the risk of passing on a genetic condition to a child, this analysis should ideally be performed before a pregnancy to help with informed decision-making about reproductive options.
In what context can sperm or egg donors be used?
The use of a sperm and/or egg donor to conceive allows many couples and individuals to access parenthood.
This is the case for some heterosexual couples, in which one or the other partner could have a diagnosis of infertility that would prevent them from being able to use their own sperm or eggs, such as azoospermia or severe ovarian failure.
This is also relevant to LGBTQ2+ couples and single parents, who need the contribution of a sperm or egg donor to be able to conceive their family.
Directed or anonymous: the different types of sperm and egg donation
There are several ways to access sperm and egg donors. Depending on whether the donation is directed or anonymous, and depending on the type of sperm or egg bank used, access to samples and available information about the donor and recontact opportunities may vary.
- In the case of directed donation, the individual who will provide the sperm or egg is known to the couple or recipient and will make a donation for a specific conception. According to the recommendations issued by Health Canada, the personal and family medical history of potential donors should be assessed to ensure that there is no significant risk of transmission of a genetic condition. In some cases, in addition to basic assessments that ensure the donor’s eligibility for fertility treatment, some clinics will also offer an expanded carrier screening test in order to assess the risk of transmission of silent genetic variants to the child. The terms of the donor’s involvement and the sharing of his or her personal information with the child will then be specific to what has been decided between the donor and the recipient(s).
- In the case of anonymous donation, the couple or recipient will choose the donor from a bank, who will only disclose certain aspects of the donor’s characteristics (the information available and the tests carried out vary depending on the bank). While some are limited to medical and family histories and basic assessments, most major U.S. banks include expanded carrier screening test results that will allow interested recipients to know if a potential donor is a carrier of one of the conditions tested. Depending on the bank, the terms and conditions of contact with the donor for children from the donation will depend on their protocols, which are generally set out when the contract is signed.
The relevance of expanded carrier screening in the context of sperm and egg donation
In the case of directed donation, if the recipient couple or individual wishes to have access to the expanded carrier screening test, it is generally indicated to assess the same set of genes in the two individuals that will provide sperm and eggs. This will allow a more accurate interpretation of the results together, and a more significant reduction in the estimated reproductive risks.
In the case of a choice from a sperm or egg bank, as mentioned above, donors will usually have already completed an expanded carrier screening test of several hundred genes. As we are all carriers of several silent genetic variants, and the number of genes tested continues to increase, it is therefore increasingly rare to be able to identify a donor who is not a carrier of any silent genetic variants.
Having identified a silent genetic variant in a donor does not exclude them. It is strongly recommended that the recipient(s) be referred for genetic counselling to assess the specific genetic risks related to the variants carried by the donor. These meetings can be followed by access to an expanded carrier screening test for the recipient if they wish. It will generally be recommended to change donor choice if a significant risk is identified.
In conclusion
Genetic compatibility is important to reduce the risk of having a child with a genetic condition, but other factors can also influence the choice of donors, depending on the criteria that are most important to the recipients, such as general appearance, ethnicity, religious affiliation, level of education, etc.
Ultimately, if your clinical and/or personal situation requires the use of a donor to conceive and you are in the process of choosing, genetic counselling can help you understand your risks of transmitting genetic conditions to your children and allow you to decide if the expanded carrier screening option makes sense for you.
Please do not hesitate to contact us if you would like to proceed with an expanded carrier screening test in the context of choosing a donor. You can also book a genetic counselling appointment for a discussion and risk assessment for a specific donor if you are unsure about this test.