What are the lab tests for Fragile X?

There are two different FMR1 DNA test lab procedures.

The FMR1 DNA test can be administered with two different lab procedures: 

  1. The Southern blot analysis test determines if the gene has a full mutation, its approximate size, whether the gene has been “methylated,” and if there is mosaicism of the gene (a mixture of different cell types). 
  2. The polymerase chain reaction (PCR) analysis can determine the actual number of CGG repeats (a pattern of DNA) that are present in the Fragile X gene. For various technical reasons, PCR has not been the test of choice to diagnose a full mutation, but is quite accurate in determining premutation and normal gene repeat numbers. However, PCR is less expensive and quicker than Southern blot, and recent advances in technology have increased its ability to identify Fragile X full mutations. PCR may thus be the only test used in the near future. 

    We have extensive information on Fragile X testing and diagnosis, including specific information to share with your doctor to help them order the correct test. 

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