Genetic Carrier Screening
A carrier screen is a genetic (DNA) blood test that investigates whether you have (“carry”) recessive gene changes – also called mutations – that could cause certain serious genetic diseases in your children. At ORM we offer genetic carrier screening to all patients undergoing fertility treatment. All genetic screening is optional, and we encourage our patients to make an informed decision.
What is recessive inheritance?
Genes are inherited from our biological parents in specific ways. One of the basic patterns of inheritance is autosomal recessive. Autosomal means that males and females carry these genes equally. To develop a recessive genetic condition, you must have inherited two copies of a mutation in that gene – one from your biological mother and one from your biological father. If you have just one recessive mutation, you are a carrier for the condition but usually do not have signs or symptoms of it. If you are a carrier, you are only at risk to have a child with the disorder if your reproductive partner happens to be a carrier of the exact same disorder. If you and your reproductive partner are carriers of the same condition, you have a ¼ (25%) chance for that condition to occur in each of your offspring.
What can I expect to learn from carrier screening?
In carrier screening your DNA is tested for mutations in a certain number of disease genes. While carrier tests will not identify all carriers of all genetic diseases, by screening many genes at once and using the most sensitive technologies, many carriers will be identified. While 30-50% of patients that we screen at ORM are found to be a carrier of at least one genetic condition, only 1-2% of couples or reproductive partners (intended parent + sperm or egg donor) are found to be carriers for the same condition and have a 25% chance to have a child with the condition.
Why is carrier screening offered as part of the infertility treatment?
For most couples having children, genetic carrier screening is unfortunately not offered by their physicians until a pregnancy has already been conceived. But testing before pregnancy allows us to discuss options for prevention of genetic disease with you, rather than coping with this information during the pregnancy or after a baby is born with the condition.
For which genetic disorders is carrier testing recommended?
The American College of Obstetrics and Gynecology (ACOG) and the American College of Medical Genetics (ACMG) recommend offering patients carrier screening for a specific, small number of genetic disorders based on their ethnic background. These include cystic fibrosis, spinal muscular atrophy, hemoglobinopathies, Tay-Sachs disease, and others depending on your ancestry. While we follow these recommendations, we also offer expanded carrier screening to our patients.
What is expanded carrier screening?
Expanded carrier screening refers to testing for a large number (generally 100 or more) genetic conditions simultaneously on one test. There are thousands of rare genetic conditions, and even expanded carrier screening cannot screen for all of these. Even so, you may consider expanded carrier screening instead of limiting your screening to those tests recommended by ACOG/ACMG because:
- You may want as much information as possible before conceiving a pregnancy;
- Testing in this manner is often more cost effective than ordering multiple individual genetic tests;
- The increasing ethnic and genetic diversity of our population is making it more difficult to offer genetic screening appropriately based on your ethnic background alone.
Which laboratory does ORM use? Which exact genes/disorders are tested for?
We use Counsyl laboratory’s Family Prep Screen. A list of the wide variety of genetic conditions on this test can be found here. Some of the conditions on the screen either have no treatment or are chronic and require lifelong management, while others can be treated early in life. Others result in intellectual disabilities. Still others have a large range of severity and their impact could be difficult to predict. Counsyl has complimentary genetic counseling available by phone and we will strongly recommend this to you to help explain your results if you are found to be a carrier.
Counsyl offers a video that explains more about autosomal recessive inheritance and carrier screening.
What if I or my reproductive partner or donor is found to carry a genetic disorder?
If you are found to be a carrier, you will probably be surprised; most often, carriers do not have any family members who are affected with the disorder they carry. Carriers are generally healthy and are not expected to have symptoms of the disease they carry, although there are a few exceptions. It is important for you to learn about the particular disease you carry and determine whether it is of concern to you. Most people who screen positive will want their reproductive partner to be screened, if they have not been already. At ORM, everyone who is found to be a carrier for a disease (or whose egg or sperm donor is a carrier) is required to have genetic counseling since the information has important implications for your family and your children. ORM strongly recommends that all desired carrier testing on both members of the reproductive couple – and genetic counseling about these results – be completed before any fertility treatment is begun.
What if my partner and I screen positive for the same gene?
If both you and your reproductive partner are carriers of the same genetic disorder, generally you have a 25% chance to have a child with that disorder. You should meet with a genetic counselor to help understand your results and the disorder for which you screened positive. If appropriate, the counselor will discuss the options available to reduce your chance of having a child with the particular condition. For example, IVF with preimplantation genetic diagnosis could be done to test embryos prior to transferring them into the uterus, to reduce the risk of having an affected child. You could also choose to have genetic testing of the fetus during pregnancy, to test the baby after birth, or not to test at all. The use of an egg or sperm donor could also be considered.
What if I am a carrier and my reproductive partner is not?
In most cases, if one partner is a carrier and the other has a negative screen for that gene, the risk to have an affected child will be quite low. However, it is very important to learn more about the accuracy of the test on the negative partner (see What does a normal carrier screen result tell me?).
What does a normal carrier screen result tell me?
Generally, a negative (normal) result means that the chance to be a carrier of that particular disorder is very low. It does not determine with certainty, though, that someone is not a carrier. The accuracy of carrier testing is influenced by the technology used to test the DNA; a person’s ethnic background; and whether there is a family history of the disease. The specific residual carrier risk (chance that someone could still be a carrier even after a normal result) is always available. Since Counsyl testing will not identify every single carrier, a known carrier may wish for their partner or donor to undergo additional DNA screening through other laboratories in order to achieve the highest accuracy possible.
No one in my family has any genetic diseases or birth defects. Do I still need carrier screening?
The vast majority of people who learn that they are carriers of a genetic disorder have no relatives with the disorder; in fact, they usually have never heard of the disorder before receiving their positive result. Recessive genes can remain hidden in families for generations because generally both members of a reproductive couple must be carriers in order for the disease to appear in a family.
What if I DO have a family history of a recessive disorder?
If you have a family member with any suspected genetic disease, or a family member who is known to be a carrier of a genetic disease, you should have genetic counseling prior to genetic screening. Not all genetic screening is created equal: using a specific genetic test or laboratory may be necessary in order to provide an accurate test for a condition that has been seen in your family. Our genetic counselors can discuss your specific family history, help determine whether testing is needed, and which test is the right test for you.