It seems that genetic testing is becoming more commonplace in the last few years. There are commercials on television advertising tests that can use a saliva swab to track your genetic ancestry. Additionally, you may have heard about genetic tests that see if you carry the gene that puts you at greater risk for breast cancer. For many years women’s health practitioners have utilized genetic testing in prenatal care. Along with this wave of newer genetic testing, prenatal carrier testing has made some advances.
Genetic carrier testing is a blood test that can tell if a person “carries” a genetic abnormality that can be passed on to a child. People who are carriers of genetic conditions do not have the genetic condition or have any symptoms; they merely carry the genetic material that could be passed on to their children. Genetic carrier testing can be offered to any individual, regardless if she is pregnant; however, in ob-gyn practices, providers often offer this testing to pregnant patients because of the potential effect on the baby. Genetic carrier testing is a one-time test and does not need to be repeated with every pregnancy. The test works by analyzing the mother’s DNA, which is something that is fixed and does not change with time.
Most genetic carrier tests screen for recessive hereditary conditions. Babies inherit genetic material from both the mother and father; each contributing half the genetic material. A carrier is a person who has one copy of the mutated gene and one copy of a normal gene. Since they have the normal gene as well, they do not have the genetic condition. However, there is a potential that this mutated gene could be passed on to a child.
The child can develop a genetic disease if he or she has two copies of a mutated gene. That means that both the mother and the father must be carriers for there to even be a chance of the couple having a child with a genetic disorder. For recessive conditions, there is a 1 in 4 chance that a child will have the condition if both parents are carriers for the condition. There is a 1 in 2 chance that the child will be a carrier, and there is a 1 in 4 chance that the child will not be a carrier or have the genetic condition. Examples of recessive inheritance conditions include diseases like cystic fibrosis, sickle cell anemia, and Tay-Sachs disease.
The American College of Obstetricians and Gynecologists (ACOG) makes guidelines for the care of patients by ob-gyns. For many years ACOG has recommended counseling patients on genetic carrier testing and offering testing to individuals of certain ethnic populations known to be at greater risk of certain genetic conditions. They also recommended offering genetic screening for cystic fibrosis, spinal muscular atrophy, fragile X syndrome, thalassemias, and sickle cell anemia, as these conditions are more common than other genetic disorders. For example, 1 out of 25 Caucasian individuals is a carrier for cystic fibrosis and 1 out of 10 African American individuals is a carrier for sickle cell anemia.
As genetic testing has become more widely available, options for genetic carrier testing have become more extensive. Expanded carrier screening is now offered by many labs, and in addition to more common genetic conditions, it also tests for more rare diseases. Most expanded carrier panels test for over 100 genetic conditions.
In 2017 ACOG expanded guidelines for genetic carrier testing to emphasize that all women, regardless of ethnic background, should be counseled on and offered genetic carrier testing. They also stated that expanded carrier screening was an acceptable method for screening patients.
As with any medical test or procedure, there are risks and benefits to having genetic carrier testing performed. The benefit of having this testing would be that the patient can find out before their child is born if he or she is at risk of having a genetic condition. For some conditions, measures can be taken to improve outcomes before the baby is born. For conditions in which the child may have disabilities, parents can be educated on the special needs of the child before he or she is born.
Genetic carrier testing has very small physical risks, as the testing is done with a simple blood draw; however, risks of screening can include emotional stress if a test result is positive for a genetic condition. This risk of stress can be amplified when the patient opts for the expanded carrier testing because when testing over 100 conditions, it is not unlikely that the test will come back positive.
When a patient receives a positive result for carrier testing, it is recommended that the father of the baby have the carrier testing. Many of the conditions tested for are very rare, and it is unlikely that both the mother and the father will both be carriers for the same condition. If the father has testing done and he does not carry any of the same genetic mutations as the mother, then there is no risk to the baby. However, if the father tests positive for the same genetic mutation as the mother, then there is a 1 in 4 chance of the baby having the genetic condition. If the father does test positive for the same condition, the couple is referred to genetic counseling and may be offered amniocentesis.
Genetic carrier testing is an important piece of prenatal and preconception care. It allows patients to be informed about their chances of having a child with a genetic disorder. If you are pregnant or thinking of becoming pregnant, it is important to have a conversation with your healthcare provider about the benefits and implications of genetic carrier testing.
Emily Nobles, WHNP. is a nurse practitioner at Atlantic Ob/Gyn located in Va. Beach and Chesapeake. Please call 757-463-1234 or visit www.atlanticobgyn.com.