Carrier screening is a type of genetic test that can tell someone if they are a carrier for a recessive genetic condition. If someone is a carrier for a recessive genetic condition, they have one copy of their gene that doesn’t work properly. The other copy of their gene for that genetic condition does work properly. However, if that person matches with a partner who is also a carrier for the same recessive genetic condition, they have a risk of passing on that genetic condition to a child. There would be a ¼ or 25% chance of passing on both partner’s non-working copy of their gene to a pregnancy, which would result in that child having the genetic condition. But what are the chances of that really happening?
What is Carrier Screening?
There are more than 1000 recessive genetic conditions that can affect a pregnancy and range in severity of symptoms. While each condition by itself is fairly rare in the general population, when combined into a group these genetic conditions account for about 20% of infant deaths and 10% of infant hospitalizations. Studies have shown that 1/300 couples are found to be a match for one of the genetic conditions tested on most expanded carrier screening panels. These recessive conditions do not typically show up in a couple’s family history, due to a couple by chance matching as carriers for the same condition.
The American College of Obstetricians and Gynecologists recommends that all women who are considering getting pregnant be offered carrier screening for these genetic conditions: cystic fibrosis, hemoglobinopathies, and spinal muscular atrophy. We recently posted a blog about cystic fibrosis, a disease of the lungs. For more information please refer to our previous blog post. Hemoglobinopathies are diseases of the red blood cells, such as sickle cell disease and alpha-thalassemia. Spinal muscular atrophy is a debilitating disease of the muscles. These particular conditions are recommended for all pregnant women because they are more common in most ethnicities compared to other recessive genetic conditions.
Should You Get a Carrier Screening?
While carrier screening should be offered to all pregnant women, it is a voluntary test. A pregnant woman (and her partner) only need to do carrier screening for any recessive genetic condition once in their life. Since carrier screening is a test that analyzes our own DNA, it does not need to be repeated as our DNA does not change. There are many testing options available through various genetic testing labs. There is typically the option of testing for only cystic fibrosis, hemoglobinopathies, and spinal muscular atrophy. There is also the option to do expanded carrier screening, which screens for 150+ recessive conditions. Every ethnic group has different risks of being a carrier for different recessive genetic conditions. Due to the various ethnic backgrounds that most people have, expanded carrier screening is designed to screen a person for the most common recessive genetic conditions of various ethnicities. In addition, there are many genetic testing labs that offer specifically Ashkenazi Jewish carrier screening panels. Those of Ashkenazi Jewish ancestry are at higher risk to be carriers for various recessive genetic conditions, and are recommended to pursue either Ashkenazi Jewish or expanded carrier screening panels.
Advantages of Genetic Testing
If a couple is found to be carriers for the same genetic conditions , there are options for both conceiving a pregnancy and after a pregnancy has occurred. For couples who have not yet conceived, they can choose to naturally conceive and test the pregnancy through diagnostic testing. There would be a 25% risk for each pregnancy to be affected by the genetic condition. There is also the option of pursuing in vitro fertilization and selecting embryos that are not affected by the genetic condition, and implanting those embryos back into the uterus. For couples that have already conceived, options include diagnostic testing during the pregnancy or testing the baby after birth.
If you are interested in pursuing carrier screening, thinking of getting pregnant, or would like more information about carrier screening, please contact AT-GC and schedule an appointment with a genetic counselor to discuss your options.