What Is Carrier Screening?
Carrier screening is testing that is done to determine whether you or your partner carry a gene mutation that could cause a serious disease or diseases in your baby.
You can have carrier screening before becoming pregnant or during your pregnancy.
What Are Genes?
Genes are made up of DNA which contains the code that makes each of us unique. Genes are packaged into structures called chromosomes and are passed from parents to children. Traits such as eye color or risk for disease are passed to our children by our genes. Each of us received one chromosome from our mother and one chromosome from our father giving us our 23 pairs of chromosomes.
Dominant And Recessive Genes
Within each chromosome pair, one chromosome is dominant and the other chromosome is recessive. Usually the dominant chromosome masks the recessive chromosome and the traits from the dominant chromosome are expressed in our characteristics.
What Is A Carrier?
A carrier is a person who has a disease trait, but does not have any physical symptoms of the disease. A carrier has a gene mutation on the recessive gene. The dominant gene outweighs the recessive gene, so while a carrier does not develop the disease, a carrier can pass on the gene with a mutation to his or her child.
Because these disorders are recessive, this means that both you and your partner must have the same gene mutation in order for your children to inherit a given recessive disorder.
Who Should Have Carrier Screening?
DNA tests are available to help a couple decide if they are carriers for the same recessive disease and if they are at risk for having a baby with that recessive condition
Carrier Screening for CF and SMA is recommended for all reproductive women:
- Cystic Fibrosis (CF) is among the most common genetic conditions that affect people regardless of their ethnicity.
- Spinal muscular Atrophy (SMA) is also among the most common genetic conditions that affect people regardless of their ethnicity.
- Effective treatments targeted for specific gene changes are available for CF and SMA.
You are at increased risk if:
- You have a genetic condition.
- You have a child who has a genetic condition.
- Your family has a history of a genetic condition.
- You are of ethnicity that has a high risk of certain genetic conditions.
Some Diseases Occur More Often In Certain Ethnic Groups
Here are the primary disorders related to ethnicity:
African, Asian, Mediterranean heritage: Thalassemia, Sickle Cell Anemia, and Cystic Fibrosis.
Ashkenazi Jewish heritage: Tay-Sachs, Canavan, Cystic Fibrosis, Familial Dysautonomia and other disorders.
European Caucasian and Hispanic heritage: Cystic Fibrosis.
French Canadian heritage: Tay-Sachs, and Cystic Fibrosis.
There are other disorders not listed here which can be screened for. Your doctor or healthcare provider will be able to provide you with more information.
Otogenetics Carrier Screening Options
Single Gene Testing: CF, SMA, Tay-Sachs
Basic Carrier Screening screens for 5 conditions or selected condition(s) included
ACOG/ACMG Carrier Screening screens for 15 genes associated with common genetic conditions
Ashkenazi Jewish Carrier Screening for 38 genes associated with prevalent genetic conditions
Pan-Ethnic Carrier Screening screens for 167 genes associated with genetic conditions
Carrier Screening for other conditions with specific personal and family indications
You will be able to decide with your healthcare provider which option is right for you.
How Is Genetic Carrier Screening Done?
If you choose to be screened, you’ll be asked to give a blood, saliva or buccal sample which is sent to the lab where your DNA is examined for evidence of genetic mutations.
Accurate fetal risk assessment requires screening of the biological father of your baby. Therefore, if you’re found to be a carrier, the father of your baby will be screened as well.
Your doctor may also screen you and your partner at the same time.
What Do The Results Tell You ?
Common Inheritance Pattern of Genetic Conditions
Most conditions screened for are autosomal recessive
Autosomal recessive: means that a disease-causing genetic change in the gene must be present in both copies of the gene in order to develop the disease condition. If one of your two copies of the gene has a disease cause genetic change, you are a carrier.
If only one parent is a carrier, then the child has a 25% of being a carrier for that disorder and a 0% chance of having the disease.
If both you and your partner are carriers of the same gene mutation, then your child:
- Has a 25% chance of inheriting one affected gene from each of you and being born with the disease.
- Has a 50% chance of being a carrier just like the parent who is a carrier.
- Has a 25% chance of not being a carrier and not having the disorder.
Some conditions screened for are X-linked recessive,
X-linked recessive: The gene is located on X chromosome, for which females have two X chromosomes while males have one X chromosome and one Y chromosome. In X-linked recessive inheritance, a female with one damaged copy of the gene in each cell is called a carrier. She can pass on the altered gene but usually does not experience signs and symptoms of the disorder. When one altered copy of the gene is inherited from an unaffected carrier mother, the male child will have the disease. There is a 50% chance that a baby will inherit the X chromosome with the altered X-linked gene from the mother; females who inherit the altered X-linked gene will be carriers, males who inherit the altered X-linked gene will be affected.
Examples of X-linked recessive conditions are Duchenne and Becker muscular dystrophy (DMD/BMD) and Glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Some conditions screened for can be semi-dominant, have variable penetrance, or variable expressivity
Semi-Dominant: Semi-dominance or incomplete dominance occurs when the physical characteristic of the child is distinct from both parents and is often intermediate to the physical characteristics of the parents. For example, in the snap dragon flower, the pink color of the flower is produced when true-bred parents of white and red flowers are crossed.
Variable Penetrance: For conditions that have variable penetrance, the age of onset of these disorders vary from person to person and in some cases an individual may not have any symptoms of the disorder.
Varying Expressivity: In genetic conditions with varying expressivity, the symptoms of the conditions are expressed differently among persons with the same genetic condition.
This means that from your results of Expanded Carrier Screening you may learn about a previously unrecognized health risk which could be important to you and your family members. Some individuals may discover during the course of Expanded Carrier Screening that they are affected by one of the less severe or late-onset diseases.
What Do The Results Mean?
A negative result suggests a reduced chance that you are carriers for the genetic conditions screened. However, a negative screening test does not eliminate the possibility that you are a carrier because there is a residual risk of being a carrier of the condition based on carrier prevalence in your ethnicity background and test sensitivity.
The chance of having an affected child for the conditions screened depends on the carrier frequency in the population and the mutations tested. It may be difficult to calculate the exact residual risk for each condition screened for in Expanded Carrier Screening because the carrier frequency of certain conditions in the general population may be unknown. It is generally recommended to assume the highest residual risk associated with your ethnicity background.
What Are Your Options If You Find Out You Are Carriers?
If you find out that you are a carrier, you have several options:
Partner Reflex Testing (for autosomal recessive conditions)
Diagnostic test confirmation
Early Screening Offers Many Advantages
For some diseases, knowing your baby is affected before birth makes it more likely that your baby can be helped by early treatment. For example, treatments targeting specific genetic changes for CF and SMA are effective.
It allows your doctor to line up the right medical specialists, who can be on hand to start treating your baby right after delivery.
For more information and patient advocacy groups, please visit our Patient Portal at www.otogenetics.com/patientportal