If you’re an expectant parent, or planning a pregnancy, you probably want to know all you can about your future family. Genetic carrier screening allows for a closer look at your genes, to see if there is a chance your baby could inherit certain genetic disorders. It’s a simple test that can help you plan with confidence.
What is fragile X syndrome?
Fragile X syndrome (FXS) is the most common inherited cause of intellectual disability. Symptoms cover a wide range, from mild to very severe. About one-third of all people with FXS also have autism. Individuals with the disorder may also have behavioral issues, such as hyperactivity, social anxiety and aggression. Though FXS occurs in both sexes, males are more frequently affected than females, and generally with greater severity.
Approximately 1 in every 3,600 boys and 1 in every 6,000 girls is born with FXS.
Watch a video to learn more about genetic carrier screening for hereditary disorders.
How is fragile X syndrome inherited?
FXS is caused by changes in the fragile X gene. The fragile X gene has a pattern of DNA, called a CGG repeat. Some individuals have a change in their gene that increases the number of repeats. This change impairs the functioning of the gene and can cause fragile X syndrome and associated disorders. A person with a certain number of increased repeats is called a carrier.
Only the mother needs to be a carrier for the baby to be at risk. When the mother is a carrier, there is up to a 1 in 2 (50%) chance the child will be affected. However, the exact risk depends on how many repeats the mother carries.
Carriers of FXS are unaffected by the disorder, but they are at risk for certain related conditions. Fragile X-associated primary ovarian insufficiency causes infertility, early menopause, and other ovarian problems. Fragile X-associated tremor/ataxia syndrome is an adult-onset neurological condition that causes tremors and problems with memory and balance.
Who can be a carrier?
Anyone can be a carrier of FXS. About 1 in 259 women in the US, across all ethnic groups, are carriers. If you have a family history of intellectual disability, autism, or infertility, then you may have a higher risk of being a carrier.
How is the test performed?
A simple test of your blood DNA (using a blood sample or a or a cheek swab sample) can determine with a high degree of accuracy whether you are a carrier of FXS.
What do the test results mean?
The results for fragile X testing fall into four categories:
|Normal||less than 45 CGG repeats||Not at risk to have a child with FXS.|
|Intermediate (gray zone)||45–54 CGG repeats||Not at risk to have a child with FXS. However, future generations may be carriers, because the number of repeats may increase with future generations.|
|Premutation (carrier)||55–200 CGG repeats||Female carriers are at risk for having a child with FXS. Carriers are also at risk for fragile X-associated disorders.|
|Full mutation||more than 200 CGG repeats||The individual may be affected by FXS. Females are at risk to have a child with FXS.|
What if I am at risk for having a child with fragile X syndrome?
If you are pregnant, prenatal diagnostic tests can tell you whether your baby is affected by the disorder.
There are also options to prevent genetic disorders prior to pregnancy. These options include in vitro fertilization, using a diagnostic test to select healthy embryos for implantation, or using donor eggs or sperm from a person who is not a carrier. Some couples choose to adopt a child. Your healthcare provider or a genetic counselor can discuss these options in greater detail.
Is genetic carrier screening required?
All testing is optional. The decision to accept or decline genetic carrier screening is completely up to you.
Talk to your healthcare provider to find out if this test is right for you.