Basics of Genetic testing in Infertility: Carrier screening
There are many different genetic tests that we can perform in reproductive medicine. These are often referred to by providers simply as all-encompassing “genetics”, which makes it difficult for patients to understand what kind of testing they had. Over the next couple of posts, we will attempt to explain some of the major methods of genetic testing used in our field and common applications for having this testing performed.
Carrier screening is a way to identify genetic conditions for which a couple’s child may be at risk. These are especially important to test because often there likely will not be a family history for these conditions. To understand this, we first need to understand the conditions necessary for the disease to present in offspring.
Each person gets one copy of DNA from their genetic mother and one from their genetic father. Carrier screening looks for autosomal recessive conditions. you need two copies of a mutated gene to have a disease which is caused by autosomal recessive conditions (there are some exceptions to this rule).
For an offspring have the disease, they would need to have 2 mutated copies of the gene (often by inheriting one mutated copy from the mother and one from the father) who are called “carriers” of these genetic variants. A carrier is someone who harbors a gene variant, but only a single copy so they do not express the disease. Remember you need to have 2 gene variants for these conditions to cause disease. However, if child inherits the mutated copy from both parents, they will then have that genetic condition. Therefore, by looking for genetic changes that are frequently known to cause these relatively common conditions we can identify potential risks to offspring. If these are identified, we can counsel patients on their risks. The couple can choose to accept those potential outcomes, or we can avoid those risks through IVF with more advanced testing which would allow us to identify embryos which would lead to an effected child and avoid transfer of those embryos. Even if you would not choose to do anything with this information, it can help pediatricians be prepared to provide necessary medical care that can drastically alter a child outcomes and quality of life.
The American College of Obstetrics and Gynecologists, as well as the American Society for Reproductive Medicine and the American College of Medical Genetics and Genomics all encourage offering carrier screening for any patient who is pregnant of desires pregnancy.
This is one of several testing modalities and preconception discussions we can have as fertility providers to improve the likelihood of having a healthy child.
