DNA testing for Fragile X, developed in 1992, is accurate and can detect carriers and fully-affected individuals. It can be ordered by any physician; the blood sample is then sent to a lab that offers the test. It usually takes several weeks to get results.

Fragile X testing: the fmr1 gene

The FMR1 gene colocalizes with a fragile site seen in FXS cells that gives this disorder its name. FXS alleles become associated with SIRT1. SIRT1, a class III histone deacetylase, deacetylates lysine 9 of histone H3 and lysine 16 of histone H4 ultimately leading to chromatin compaction and gene silencing. Image Credit: PLoS Genetics, 3/2008. Dr. Marian L. Miller (Journal-Cover-Art.com)

Because symptoms of Fragile X can be subtle, especially in young children, and because it is so frequent in the general population (1 in 4000 males and 1 in 6000 females), Fragile X testing should be considered for any individual with signs of autism or unexplained developmental delay or intellectual disabilities.

Most major U.S. medical centers offer the Fragile X test. It may cost several hundred dollars but is usually covered by health insurance. Prenatal testing with chorionic villus sampling or amniocentesis allows diagnosis of FMR1 mutation while the fetus is in utero and appears to be reliable.

For more information about testing, talk to your doctor or genetic counselor. You can also browse this map of U.S. Fragile X Clinics

  • Diagnosis Details

    Cytogenetic analysis for Fragile X syndrome was first available in the late 1970s when diagnosis of the syndrome and carrier status could be determined by culturing cells in a folate deficient medium and then assessing for “fragile sites” (discontinuity of staining in the region of the trinucleotide repeat) on the long arm of the X chromosome.[25] This technique proved unreliable, however, as the fragile site was often seen in less than 40% of an individual’s cells. This was not as much of a problem in males, but in female carriers, where the fragile site could generally only be seen in 10% of cells, the mutation often could not be visualised.

    Since the 1990s, more sensitive molecular techniques have been used to determine carrier status.[25] The fragile X abnormality is now directly determined by analysis of the number of CGG repeats using polymerase chain reaction (PCR) and methylation status using Southern blot analysis.[4] By determining the number of CGG repeats on the X chromosome, this method allows for more accurate assessment of risk for premutation carriers in terms of their own risk of fragile X associated syndromes, as well as their risk of having affected children. Because this method only tests for expansion of the CGG repeat, individuals with FXS due to missense mutations or deletions involving FMR1 will not be diagnosed using this test and should therefore undergo sequencing of the FMR1 gene if there is clinical suspicion of FXS.

    Source: wikipedia link

  • What are the chances of passing Fragile X from mother to child?

    When a woman is a carrier of Fragile X, her chances of passing the mutation on to her children depend on the length of her own premutation.  This article was written by experts in Fragile X syndrome and prenatal diagnosis.

    Expansion of the Fragile X CGG Repeat in Females with Premutation or Intermediate Alleles
    Am J Hum Genet. Feb 2003; by Sarah L. Nolin,1 W. Ted Brown,1 Anne Glicksman,1 George E. Houck, Jr.,1 Alice D. Gargano,1 Amy Sullivan,2 Valérie Biancalana,3 Karen Bröndum-Nielsen,4 Helle Hjalgrim,4 Elke Holinski-Feder,5 Frank Kooy,6 John Longshore,7 James Macpherson,8 Jean-Louis Mandel,3 Gert Matthijs,9 Francois Rousseau,10 Peter Steinbach,11 Marja-Leena Väisänen,12Harriet von Koskull,13 and Stephanie L. Sherman2

Diagnosis References

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