When you and your partner make an appointment for genetic testing, you will most likely be prompted to fill out some paperwork and answer questions regarding your family’s health history. You can have genetic testing done either by having your blood or saliva tested. After the specimen is collected, it will be sent to a lab for testing.
Most often, a genetic counselor will help you to determine who is at a greater risk for having a defective gene – either you or your partner – and if that person is cleared, there will be no further need for genetic testing. If, however, that person is identified as being a carrier, then the second partner should also be tested to determine the likelihood of passing along a disorder to a child.
Your genetic counselor will go over results with you and determine the odds of you and your partner conceiving a child with a disorder. If both parents are identified as carriers, then there is a 25% chance that your baby will have the disorder, while the likelihood that the child will be a carrier (like the carriers parents, he or she will have the gene for the disorder but display no symptoms) is 50%. If one parent is a carrier but the other does not have the gene for a particular disorder, then there is a 50% chance that the child could become a carrier, but 0% chance that he or she will have that disorder. However, it’s important to note that there is never a guarantee that tests are entirely conclusive; there’s always a small chance that a mutation could have been overlooked because it’s impossible for testing to be 100% thorough.
Likewise, it’s also possible to have either false positives or false negatives in carrier screening.1 The bottom line is that carrier screening is in fact quite complex. It’s not as simple as looking for one particular genetic mutation to determine whether someone is a carrier. For cystic fibrosis alone, the most inclusive panels available test the blood or saliva sample for 97 of the most common mutations linked to the disorder, but there’s a chance that a person could have any one of 2,000 possible mutations. Most tests identify 95 to 99 percent of carriers, which is why a genetic counselor is best for helping you to pinpoint your odds for passing on a mutation as closely as possible.2 [avafootnote]
- The American College of Obstetricians and Gynecologists. (2015). Preconception Carrier Screening. Retrieved from http://www.acog.org/-/media/For-Patients/faq179.pdf?dmc=1&ts=20151009T1204498329 ↩
- Revelant, Julie. (2012, March 7). 5 things you should know about genetic testing. Fox News. Retrieved from http://www.foxnews.com/health/2012/03/07/5-things-should-know-about-genetic-testing/ ↩