But no one in my family has this condition, how can I be a carrier of it?
This is a common question to come up when someone finds out they are a carrier of a certain condition. It is natural to think back to the family history to figure out where this may have come from. However, most of the conditions we end up being carriers of are rare and/or are unlikely to have impacted any of our relatives because of autosomal recessive inheritance pattern. It is important to know that being a carrier is normal. We are all carriers for at least one genetic condition like cystic fibrosis or sickle cell disease. Usually, being a carrier means you do not have any symptoms of the condition, but your children could, if your partner is also a carrier. Since carriers are usually healthy individuals, most people do not know they are a carrier until they do certain blood tests that check for carrier status or they have a child with that condition.
What does it mean to be a carrier?
We all have two copies of each gene. We inherit one copy from our mom/egg donor and the other from our dad/sperm donor. A carrier is someone who has one gene copy with a pathogenic variant or mutation that causes the gene not to work. Since a carrier has the other gene copy that does work, they usually do not have the symptoms associated with the condition they are a carrier for. A carrier could pass on the gene that does not work to their future children. As long as their partner is not also a carrier, then their children would not be expected to have the condition either. However, if their partner is a carrier, then each time they have a pregnancy there is a 25% chance for that pregnancy to have the condition and symptoms. This is referred to as autosomal recessive inheritance.
There are some conditions with an X-linked inheritance pattern. X-linked conditions are caused by a gene that doesn’t work properly located on the X chromosome. In order for our genes to fit into our cells (where they are located), they have to package themselves into these structures called chromosomes. Genetic males have one Y chromosome and one X chromosome which means they have only one copy of each gene on the X chromosome. If that one copy of the gene is not working properly, then their bodies aren’t able to do the function of that gene resulting health complications. Genetic females, however, have two X chromosomes. If one copy of their gene isn’t working, then they have another copy of that gene on their other X chromosome to carry out the necessary function. Genetic females are usually just carriers of x-linked conditions; however, there are cases where females can have symptoms of the condition. It is important for female carriers to follow up with a health care provider.
For x-linked inheritance, there is a 50% chance a genetic female could pass on the gene that doesn’t work properly to their children. For their daughters, there is a 50% chance they are carriers; for their sons, there is a 50% chance they are affected with the condition.
What does someone do if they find out they are a carrier of an X-linked condition or the couple are both carriers?
There are a few options:
Prevent having a pregnancy with the condition by using in-vitro fertilization with preimplantation genetic testing (IVF with PGT-M).
Use a donor that is not a carrier for egg or sperm.
Use a donated embryo from a couple, who are not carriers of the condition.
Conceive without intervention from assisted reproductive technology and test the pregnancy with chorionic villi sampling (CVS) or amniocentesis. If the pregnancy is found to have the condition, then the options of adoption, termination, or parenting are available.
Adopt a child without the condition.
Decide to not have children given the chances involved.
Conceive without any additional testing or evaluation and test the baby after birth.
All of these options are valid. What makes sense for one family does not make sense for another. Some people are glad to have found out what they are a carrier for. They can use technology to help bring a healthy child into their family. Other people do not find this information helpful and want to bring a child into their family regardless or that the available options are too costly. No matter how you feel about this information, it is out there.
If someone is interested in this information, then seeing a genetic counselor may be most helpful since there are many options for carrier screening.
Want to see a genetic counselor? You can find them at: https://findageneticcounselor.nsgc.org/.
Resource:
https://www.nature.com/articles/s41436-021-01203-z
* This blog constitutes general information about genetic testing and medical screening. This blog does not offer or provide medical advice or diagnosis, and nothing in this blog/webinar should be construed as medical advice or diagnosis. Do not rely on the information in this blog/webinar to make medical management decisions. Please consult with a medical professional before making those decisions. Do not delay in seeking professional medical advice if you think you have a medical concern. Do not disregard professional medical advice based on any information received in this blog.
