Fragile X syndrome

Diagnosis and Testing

Is there newborn testing for fragile X syndrome?

Testing of the FMR1 gene is available for infants/newborns suspected to have fragile X syndrome. The same blood test that is done for adults is done for children and infants/newborns. The "gold standard" for fragile X syndrome testing has been polymerase chain reaction (PCR) testing to determine the number of CGG repeats and Southern blot analysis, which is another method used to detect the number of repeats that can also determine whether the gene is methylated (turned off) or not. This type of testing must be ordered by a physician or genetic counselor who can interpret the results for the patient and their family.

Fragile X syndrome can be diagnosed prenatally but confirmation of an expanded FMR1 gene in the family is required before testing of at-risk pregnancies can take place. Prenatal testing for fragile X syndrome and be done by testing cells from the amniotic fluid (the liquid in the sac that contains the baby) obtained by amniocentesis (a procedure where a needle is inserted with ultrasound guidance into the belly of a pregnant woman to get amniotic fluid). Another option is to obtain cells for testing by a technique called CVS (chorionic villus sampling), in which a needle is inserted through the belly or vaginally to obtain a tiny bit of the placenta. These cells from the placenta have the same genetic makeup as the baby, and can be tested to determine the number of CGG repeats in the FMR1 gene. However, the test results from cells obtained by CVS need to be interpreted with caution, because methylation status (whether a gene is turned off or not) has not yet been determine at that point in prenatal development. Follow up amniocentesis may be required to clarify an unclear or inconclusive test result by CVS. The collection of cells through amniocentesis or CVS must be done by a physician and the genetic testing must be ordered by a physician or genetic counselor who can interpret the results for the patient and their family. To find a genetic counselor, please visit www.nsgc.org and click the "Find a Genetic Counselor" link to locate a provider in your area.

https://www.acmg.net/Pages/ACMG_Activities/stds-2002/fx.htm

http://www.ncbi.nlm.nih.gov/books/NBK1384/

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