Diagnosis and Testing
How do I get tested for trisomy X?
Trisomy X can be diagnosed by chromosome analysis before a baby is born (prenatally) or after a baby is born (postnatally). The most common type of chromosome analysis used to diagnose trisomy X is known as a karyotype, which is essentially an organized image of the chromosomes within a cell obtained by microscopic evaluation.
A karyotype is most often obtained prenatally on a sample of cells from amniotic fluid (via a procedure known as amniocentesis) or placental tissue known as chorionic villi (via chorionic villus sampling). There is also noninvasive prenatal screening tests such as cell-free fetal DNA testing (a blood test performed on the mother during pregnancy) that can identify pregnancies at increased risk for trisomy X, but these are not diagnostic and should not be relied on as final test results.
If a karyotype is performed on an individual postnatally, it is most often done on a blood sample.
If you wish to obtain more information about the specific testing used to diagnose trisomy X, consider making an appointment with a genetic counselor. To find a local genetic counselor, use the Find a Genetic Counselor search tool on the National Society of Genetic Counselors' website.
More Diagnosis and Testing Content
Is there newborn testing for trisomy X?
As of October 2016, Down syndrome is not on the Recommended Uniform Screen Panel (RUSP). The RUSP is created by the Health Resources and Services Administration, and states use this list to guide what conditions they screen for on newborn screening. It should be noted that babies with trisomy X are expected to be healthy newborns and not require any immediate medical intervention.
Is there more than one test for trisomy X?
There is more than one test for trisomy X, but medical experts agree that a diagnosis should be confirmed by a test known as a karyotype. A karyotype is essentially an organized image of the chromosomes within a cell obtained by microscopic evaluation. It is very important to remember that a prenatal screening performed on maternal blood known as a non-invasive prenatal testing ("NIPT") or cell-free fetal DNA screening test are not diagnostic. Therefore, a pregnancy which has been considered high risk or at increased risk for trisomy X by these screens needs confirmatory testing by karyotype before the diagnosis can be made. It is also important to know that there are other chromosome tests such as chromosomal microarray and fluorescent in situ hybridization (FISH) that can diagnose trisomy X. A chromosomal microarray gives much more detail about an individual's chromosome makeup, but is not more sensitive at diagnosing or ruling out trisomy X and is a more expensive test than karyotyping. Furthermore, while microarray and FISH can diagnose or rule out trisomy X, they often cannot determine if mosaicism is present. Only a karyotype can determine this important piece of information.
Who else in my family should I test for trisomy X?
Because trisomy X does not run in families, if one family member has been diagnosed with trisomy X, it is not recommended that other family members be tested for this condition.