A person who has a disease-causing variant — also known as a mutation — in one of their two copies of a particular gene is known as a carrier. Carrier screening for specific genetic conditions is a routine part of prenatal care, but patients and providers are increasingly recognizing the importance of screening before pregnancy. Understanding your carrier screening options and the benefits of expanded carrier screening is the first step in deciding what is right for you and your future children.
What Is Carrier Screening?
Carrier screening is a form of genetic testing — usually a simple blood or saliva test — that determines if prospective parents are carriers for certain heritable genetic diseases. It mostly tests for diseases with autosomal recessive inheritance, which means both prospective parents must carry mutations in the same gene to be at risk for having a child with that disease. When both parents are carriers for the same disease, their offspring have a 25 percent chance of inheriting the disease. Carriers of recessive diseases typically do not exhibit symptoms, and there is usually no trace of the disease in their family history either, so carrier screening is incredibly important.
With recent advances in genetic testing, there are now three different types of carrier screening tests — ethnicity-based carrier screening, pan-ethnic carrier screening and expanded carrier screening. These forms of carrier screening differ depending on who they are offered to, how the test is done, and most importantly, how many different diseases are screened.
As with most genetic testing, the cost of testing depends on which test you choose and what your insurance company covers. Some companies may be able to help you determine what your insurance covers and may offer financial aid programs.
Who Should Undergo Carrier Screening and When?
Carrier screening is for any prospective parent who wants to know their risk of passing on a genetic disease to future offspring. While everyone should consider carrier screening, genetic counselor Shivani Nazareth cautions those whose partners aren’t available for testing to think through the ramifications of carrier screening. “For recessive diseases in particular, the results only make sense in pairs. In other words, the risk estimate requires two biologic parents,” says Nazareth.
According to Nazareth, carriers have more options if they know their results prior to pregnancy. For example, carrier couples could use egg or sperm donor to decrease their risk. They could also undergo preimplantation genetic testing — testing an embryo prior to implantation — to reduce the risk that their child will inherit the disease in question. If carriers get their results during pregnancy, they have the option of prenatal diagnosis to monitor how their baby is developing.
People with a family history of a specific genetic disease should consider meeting with a genetic counselor prior to having carrier screening. A genetic counselor can ensure that your carrier screening test includes the specific variant or mutation that caused the genetic disease in your family and can provide you with truly personalized information.
Ethnicity-Based Screening and Pan-Ethnic Screening
Ethnicity-based carrier screening is offered to people with specific ethnic backgrounds that have a higher risk for certain genetic diseases. For example, people with African heritage are offered carrier screening for sickle cell anemia, and people with Eastern European Jewish ancestry are offered screening for Tay-Sachs and other diseases. This ultra-targeted carrier screening doesn’t always properly diagnose people with mixed or unknown ethnicity, and it only tests for a limited number of diseases.
The American College of Obstetrics and Gynecology (ACOG) recognizes that some genetic diseases occur in all ethnicities, so they recommend that everyone undergo a pan-ethnic carrier screening. While pan-ethnic carrier screening offers risk assessment to more ethnic groups, testing is still limited to a small number of well-understood genetic diseases.
The Benefits of Expanded Carrier Screening
Expanded carrier screening is a form of DNA testing that tests for variants in hundreds of genes at the same time, regardless of ethnicity. The benefits of expanded carrier screening include a more thorough determination of risk for a greater number of diseases. Many companies offer expanded carrier screening tests, but the number of mutations and genes tested for can differ between companies. Genetic counselors can help people decide which form of carrier screening, if any, is right for them.
In today’s world, with an increasing number of people reporting mixed ancestry and many people not identifying with a single race or ethnicity, expanded carrier screening offers more complete information and information without bias.
The majority of fertility specialists offer expanded carrier screening to their patients prior to pregnancy, while most OB/Gyn specialists offer ethnic-based or pan-ethnic carrier screening during the pregnancy.
Carrier screening — whether ethnicity-based, pan-ethnic or expanded — can be one of the first steps to ensure a healthy child.
Kathleen Fergus, MS LCGC is a freelance medical writer in northern California. She is also a genetic counselor with over twenty years clinical experience with an extensive background in many medical specialties including oncology, prenatal screening, carrier screening, DNA testing methodologies, newborn screening, public health genetics and rare genetic diseases. Her interest in genetics, health communications strategies and health literacy evolved into a freelance medical writing career. She has written for VeryWell, Exploragen, ThinkGenetic and many other publications.